## Global trade network analysis with Python: central players in bluefin tuna and large aircraft

Network analysis provides useful insights into complex bilateral trade data. Two methods are presented for calculating with Python each country’s influence in the global trade network for individual goods. Related concepts in graph and international trade theories are discussed.

##### Modern goods have complex trade networks

The things we buy increasingly travel long distances and from scattered origins before they reach us. Take one man’s repeatedly failed attempt to build a toaster (from scratch). Over several decades companies have changed their production techniques, relying on global value chains, for example, to keep costs low. These changes have gradually contributed to long-term growth in global trade.

The more deeply a country becomes involved in global trade, and in global supply chains in particular, the more subjected its economy becomes to changes abroad. This can be good; historically many powerful cities began as ports. However, the potential for higher returns from servicing foreign demand carries with it increased risk of economic contagion.

It is not hard to imagine how global supply chain connections transmit effects from other countries. If a strike in France delays the delivery of a crucial intermediate good, it may cause an assembly line stoppage in Taiwan. On an aggregate level, the results do not necessarily average out, and can result in vast shifts of wealth.

It may therefore prove useful to examine the complex networks of global trade using the tools provided largely by graph theory. As an example, let’s start with a graph of the global trade of tires in 2012.

Each country that exported or imported automobile tires in 2012 is represented above by one node labeled with its three letter country code (for example Germany is DEU). The precise location of a node on the graph is not critical (it is often arbitrary), but generally countries more central to the trade of tires are closer to the center of the network. Likewise, countries are generally graphed near their largest trading partners.

Each trading relationship is shown on the graph as an edge (a line connecting two nodes). If France exports tires to Aruba, the graph will include an edge connecting the two nodes labeled FRA and ABW. Trade network edges are considered directed, as the flow of goods has a direction (either imports or exports).

##### Rat’s nest or Rorschach?

You may look at the above ‘visualization’ and simply see a rat’s nest. This is a correct interpretation. The graph shows overall complexity in the trade network, not individual bilateral relationships (there are more than 4400 edges in this network). Indeed the automobile tire trade network is particularly large and dense. Many countries currently produce internationally competitive tires and all countries use them and import at least some. In fact, the average country imports tires from many other countries. A graph of the resultant trade network is reminiscent of a gray blob and practically as useful.

More useful, however, are individual metrics of network structure. For example, which countries tend to trade only with a select subgroup of other countries? Which goods are traded in networks where one country dominates trade? These questions relate theoretically to the respective graph theory concepts of clustering and centrality.

Let’s take a look at how the Python programming language can be used to measure centrality in trade networks, and discuss two specific measures of centrality.

#### Python for trade network analysis

What follows is a more technical segment with sample code for trade network analysis of using Python 2.7.

###### Let’s start by importing the packages

In [1]:

```import networkx as nx
import csv
import numpy as np
import matplotlib
import matplotlib.pyplot as plt
from matplotlib import cm
from mpl_toolkits.axes_grid1 import make_axes_locatable
%matplotlib inline```

We will rely heavily on NetworkX and give it the short name nx. Numpy is used to do certain calculations, and matplotlib helps with the visualizations.

##### Load the data and build the network

The example uses cleaned bilateral UN Comtrade trade data for scrap aluminum exports in 2012. The data follow the HS2002 classification system at the six-digit level of aggregation, and are sourced from WITS (subscription required for bulk download). Data are read from a csv file with the equivalent of three ‘columns’: the exporting country code, the importing country code, and the inflation-adjusted US Dollar value of exports in the one year period.

Data from the csv file are read line by line to build the network quickly. NetworkX is used to build the network, which is called G according to convention,  as a series of edges.

###### Read the data and build a network called G

In [2]:

```G = nx.DiGraph() # create a directed graph called G

# Loop reads a csv file with scrap aluminum bilateral trade data
with open('760200_2012.csv', 'r') as csvfile:

csv_f.next()

# Now we build the network by adding each row of data
# as an edge between two nodes (columns 1 and 2).
for row in csv_f:

Let’s look at a specific bilateral trade relationship to verify that the new network, G, is correct. Exports of scrap aluminum from the U.S. to China should be quite large in 2012.

###### Check individual trade flow (edge)

In [3]:

```usachnexp = G.edge['USA']['CHN']['weight']
print 'USA 2012 scrap aluminum exports to China, in USD: ' + str(usachnexp)```
`USA 2012 scrap aluminum exports to China, in USD: 1199682944`
##### Central players can affect the market

Now that the network has been built, we can use indicators from graph theory to identify potential weaknesses and risks in the network’s structure. In this example, we will look for the presence of dominant countries in the trade network. Dominant importers or exporters have the ability to influence supply and demand and therefore price. These dominant countries are highly influential players in the trade network, a characteristic measured in graph theory as centrality.

There are several measures of centrality and two are discussed briefly in this post. The first is eigenvector centrality, which iteratively computes the weighted and directed centrality of a node based on the centrality scores of its connections. The example below scores each importer country as a function of the import-value-weighted scores of its trading partners. That is, an importer is considered influential to a trade network (receives a high eigenvector centrality score) if it imports a lot from countries that are also influential. Mathematically, eigenvector centrality computes the left or right (left is import centrality, right is export centrality) principle eigenvector for the network matrix.

See the NetworkX documentation for questions on the code or this for more details on the the math.

###### Calculate eigenvector centrality of imports

In [4]:

```# Calculate eigenvector centrality of matrix G
# with the exports value as weights
ec = nx.eigenvector_centrality_numpy(G, weight='weight')

# Set this as a node attribute for each node
nx.set_node_attributes(G, 'cent', ec)

# Use this measure to determine the node color in viz
node_color = [float(G.node[v]['cent']) for v in G]```
##### Calculate total exports

Next we calculate each country’s total exports of scrap aluminum in 2012 as the sum total of its individual exports (edges) to other nodes. In the script, total export data is assigned as a node attribute and set aside to be used as the node size in the visualization.

###### Calculate each country’s total exports

In [5]:

```# Blank dictionary to store total exports
totexp = {}

# Calculate total exports of each country in the network
for exp in G.nodes():
tx=sum([float(g) for exp,f,g in G.out_edges_iter(exp, 'weight')])
totexp[exp] = tx
avgexp = np.mean(tx)
nx.set_node_attributes(G, 'totexp', totexp)

# Use the results later for the node's size in the graph
node_size = [float(G.node[v]['totexp']) / avgexp for v in G]```
##### Visualization of the scrap aluminum network

NetworkX works well with matplotlib to produce the spring layout visualization. It is another rat’s nest, but you may notice a different color on one of the medium-sized nodes.

###### Create graph using NetworkX and matplotlib

In [6]:

```# Visualization
# Calculate position of each node in G using networkx spring layout
pos = nx.spring_layout(G,k=30,iterations=8)

# Draw nodes
nodes = nx.draw_networkx_nodes(G,pos, node_size=node_size, \
node_color=node_color, alpha=0.5)
# Draw edges
edges = nx.draw_networkx_edges(G, pos, edge_color='lightgray', \
arrows=False, width=0.05,)

nx.draw_networkx_labels(G,pos,font_size=5)
nodes.set_edgecolor('gray')

plt.text(0,-0.1, \
'Node color is eigenvector centrality; \
Node size is value of global exports', \
fontsize=7)
plt.title('Scrap Aluminum trade network, 2012', fontsize=12)

# Bar with color scale for eigenvalues
cbar = plt.colorbar(mappable=nodes, cax=None, ax=None, fraction=0.015, pad=0.04)
cbar.set_clim(0, 1)

# Plot options
plt.margins(0,0)
plt.axis('off')

# Save as high quality png
plt.savefig('760200.png', dpi=1000)```
##### Central players on the demand side: scrap aluminum and bluefin tuna

The graph above shows plenty of large exporters (the large nodes) of scrap aluminum in 2012, including the US, Hong Kong (HKG), and Germany (DEU). The demand of one country in the network, however, actually dominates the market. In 2012, the booming Chinese economy was purchasing large quantities of industrial metals, including scrap metals. The surge in demand from China was enough to cause global price increases and lead to increased levels of recycling. Since 2012, however, Chinese imports of scrap aluminum have nearly halved, as has the market price of aluminum. The recent boom-and-bust cycle in scrap aluminum prices has a single country of origin but global ripples; the downturn generates domestic consequences for the large exporters and reduces the financial incentives for recycling.

The central influence of China in the 2012 scrap aluminum trade network is captured by its high eigenvector centrality score (node color in the graph above). We can also easily infer the out sized influence of China from a more simple measure–the high value of its imports relative to other countries. Centrality metrics, of which there are many, often prove useful in nuanced cases.

Another example of a central influence on a trade network can be found in Japanese demand for bluefin tuna. As shown below, Japan has very high eigenvector centrality for imports of this key ingredient in many sushi dishes.

Australia (AUS) dominates bluefin tuna exports, but by eigenvector import centrality Japan (JPN) is the influential player in the market. The first Tokyo tuna auction of 2013 saw one fish fetch a record 1.76 million USD. Indeed in 2012 Japan imported more than 100 times as much bluefin tuna as the second largest importer, Korea.

Like scrap aluminum, the story here follows the familiar boom-and-bust cycle; prices for bluefin tuna have returned to lower levels since 2012. The structure of the trade network, with one central player, introduces a higher level of price volatility. During a downturn in prices, this transmits financial consequences to fishermen throughout the world.

##### Supply-side influential players: large aircraft production

Trade network analysis can also help to identify influential exporters of goods. Cases that come to mind are rare earth minerals found only in certain countries, or large and complex transportation equipment. Commercial aircraft manufacturers, for example, are limited (unfortunately this may have more to do with subsidies than limited supply of technological prowess). Very large aircraft production is dominated by two firms: Airbus, with production sites primarily in France and Germany, and U.S. competitor, Boeing.

Instead of using eigenvector centrality to measure the influence of each exporting country in the large aircraft global trade network, let’s use a more simple method called outdegree centrality. We compute outdegree centrality for each country, $i$, as its number of outgoing (exporting) connections, $k^{out}_i$, divided by the total number of possible importers, $(v - 1)$:

$c^{out}_D (i) = k^{out}_i / (v - 1)$.

You can think of this measure as the share of importers that are serviced by each exporter. Nodes with a high outdegree centrality are considered influential exporters in the network.

###### Calculate outdegree centrality

In [7]:

`oc = nx.out_degree_centrality(G) # replaces ec in the above`

As expected, France, Germany, and the U.S. receive high outdegree centrality scores. There simply aren’t many alternative countries from which to buy your large aircraft. Beyond lack of choice for buyers, central exporters in a trade network may introduce (or represent) vulnerability and barriers to competition.

##### Network structure and (preventing) domestic consequences

Global trade is increasingly complex. Open economies are vulnerable to supply and demand shocks from the other countries in their trade network. The structure of the trade network itself determines in part the level of vulnerability and how and where supply and demand shocks may be transmitted. Certain trade networks, such as those for scrap aluminum or bluefin tuna, face dominant consumers and additional price volatility. Networks can also be subject to supply-side market structure issues, such as the virtual duopoly with very large aircraft.

Hindsight makes bubbles more visible; we easily find the previously missed warning signs once we know where to look. Decision makers aim for early detection of vulnerabilities, but face a geographically growing set of possible sources. Network analysis tools, such as centrality, can be applied to existing sets of complex bilateral trade data to provide new insight in the search for today’s warning signs. Such nontraditional tools may prove increasingly useful in a world where an individual is not capable of building a toaster from scratch, yet they sell down the street for \$11.99.

###### For fun:

The Toaster Project

###### Some references and further reading on networks and graph theory:

Easley and Kleinberg (2010) Networks, Crowds, and Markets: Reasoning about a Highly Connected World

Jackson (2010) Social and Economic Networks

De Benedictis (2013) Network Analysis of World Trade using the BACI-CEPII dataset

Nemeth (1985) International Trade and World-System Structure: A Multiple Network Analysis

###### Some python related resources:

Anaconda distribution for python

NetworkX

ComputSimu: Networks 1: Scraping + Data visualization + Graph stats (more useful code here)

## Dashboard update: Jobs data and new uncertainty

#### Dashboard PDF file:

##### Dashboard Update Summary:

Jobs data for April showed payrolls continue to grow, but at a slower rate. Wage data was strong, however, the labor force participation rate gave up much of its recent improvement. Uncertainty surrounding markets and economic policy seems to have increased in the recent week, and fewer economists now predict a Fed rate hike in June. U.S. equity markets were down for the second consecutive week, while corporate bond yields rose and treasury yields fell. Recent data showed improvement in the trade balance from the weaker dollar, however, the recent depreciation trend has also become less certain.

##### Jobs Report showed slower jobs growth but wage improvement

The U.S. added 160,000 jobs in April, compared with 208,000 in March and 233,000 in February (both previous months were also revised downward). By sector, much of the growth came from the services side, on an annualized basis. Construction jobs, which make up less than five percent of nonfarm payrolls, were up 4.1 percent, while mining and logging jobs continued their decline and are now down more than fifteen percent over the past year (this is the smallest industry sector shown in the figure below, and represents only 0.4 percent of nonfarm payrolls). Weekly data on new jobless claims, as of April 30, showed still very low, but slightly increased, levels.

The latest jobs report shows continued improvement in both nominal and real wages in practically all sectors. Nominal wages increased most rapidly over the past year in financial services, information services, and leisure and hospitality. On average, wages from the goods sector are higher, largely as a result of low-wage service-sector jobs in leisure and hospitality.

##### Equity and Bond market conditions deteriorated

Equity markets were down for the second straight week. The S&P 500 was down 0.4 percent, the Nasdaq composite index was down 0.8 percent, and the Dow Jones industrial average was 0.2 percent lower. Volatility was higher during the week, and the VIX closed Friday at 14.7. The Shiller index of price to earnings ratios was up to 26.02 percent in April from 25.54 in March. Corporate bond yields ticked up during the week. The Merrill Lynch index of junk bond yields was up to 7.56 percent. Ten year treasury yields fell to 1.79 percent.

##### Economic policy uncertainty improved in April but may revert

Economic policy uncertainty, as measured by Baker, Bloom, and Davis, fell sharply in April, as there was little speculation of Fed action at the April meeting. However, I expect this index to bounce back; uncertainty will increase as the Fed June meeting and Brexit grow closer.

##### Oil was down on the week, while April food prices increased

Oil prices closed lower on the week. The U.S. measure of crude oil prices, West Texas Intermediate crude front-month contracts, fell 2.7 percent during the week, to \$44.66 a barrel. World food prices from the Food and Agriculture Organization (which I half-jokingly also use as a proxy of political instability) ticked up slightly in April, but remain low.

##### A weaker dollar improved the trade balance in March

The Fed’s trade-weighted dollar broad index against major currencies fell last Friday (April 29–past week data is released on Mondays) to its lowest level since May 2015. The year-to-date rapid depreciation of the dollar has cut import quantities, as further evidenced in the March data on trade. The trade deficit, which remains roughly 2.2 percent of GDP, improved to -40.4B in March. However, more recent foreign exchange data shows uncertainty about recent depreciation trends. The dollar was stronger against nearly all major trading partners during the past week, notably 1.2 percent against the British pound, 2.76 percent against the Canadian dollar, 3.16 percent against the Australian dollar, 4.5 percent against the Turkish lira, 3,86 percent against the Mexican peso, and 4.3 percent against the South African rand.

## Machine Reading IMF Data: Data Retrieval with Python

Updated November 16, 2016

### Introduction

The International Monetary Fund (IMF) Statistics Department (STA) allows API access to their economic time series. Well-known datasets such as International Financial Statistics (IFS) can be machine read through the API. This example will use Python to retrieve Direction of Trade Statistics (DOTS) data from STA’s JSON RESTful Web Service so that we can determine the United States’ share of world exports over the past 50 years.

The IMF knowledge base provides more information on the three avaiable API formats and IMF data services. For more information on the work of STA, see their PDF annual report (PDF), STA at a glance 2015.

### Gathering series and dimension information

First, we will need to import the requests and pandas libraries. These will allow us to read json data, open urls, and request information from the web.

#### Libraries

In [1]:
```# Import libraries
import requests
import pandas as pd
```

Since we are using the JSON RESTful API, we start by using the ‘Dataflow’ endpoint URL to look at what series are available and find the series id of interest. The full output is long, so I’ve removed the data unrelated to this example. The IMF has many more series than what is shown below.

#### Find Series Name

In [2]:
```# Find the series id and text name.
url = 'http://dataservices.imf.org/REST/SDMX_JSON.svc/Dataflow/'
seriesids = requests.get(url).json()
df = pd.DataFrame(seriesids['Structure']['Dataflows']['Dataflow'])
for x in range(6, 13):
items = (str(df['@id'][x]), str(df['Name'][x]['#text']))
print ': '.join(items)
```
```DOT: Direction of Trade Statistics (DOTS)
FSIREM: Financial Soundness Indicators (FSI), Reporting Entities - Multidimensional
CDIS: Coordinated Direct Investment Survey (CDIS)
GFS01M: Government Finance Statistics (GFS 2001) - Multidimensional
GFS01: Government Finance Statistics (GFS 2001)
BOP: Balance of Payments (BOP)
BOPAGG: Balance of Payments (BOP), World and Regional Aggregates
```

We found above that the id for Direction of Trade Statistics is DOT. We can use this id to read notes about the series. We will next need to identify the dimensions of the data. For example, direction of trade data is based on a home country a flow and measure and a counterpart country. The data also has multiple frequencies and units of measurement. All of this information will be needed to later make our data request.

#### Find Series Details and Description

In [3]:
```# Annotations for the series
url = "http://dataservices.imf.org/REST/SDMX_JSON.svc/DataStructure/DOT"
dotstruct = requests.get(url).json()
df = pd.DataFrame(dotstruct['Structure']['KeyFamilies']\
['KeyFamily']['Annotations'])
for x in range(0, 7):
items = (str(df['Annotation'][x]['AnnotationTitle']), \
str(df['Annotation'][x]['AnnotationText']['#text']))
print ': '.join(items)
```
```Latest Update Date: 04/26/2016
Name: Direction of Trade Statistics (DOTS)
Temporal Coverage: Monthly and quarterly data are available starting 1960. Annual data are available starting 1947.
Geographic Coverage: DOTS covers 184 countries, the world, and major areas.
Methodology: Guide to Direction of Trade Statistics, 1993. See Documents tab.
Definition: The <B>Direction of Trade Statistics (DOTS)</B> presents current figures on the value of merchandise exports and imports disaggregated according to a country's primary trading partners. Area and world aggregates are included in the display of trade flows between major areas of the world. Reported data is supplemented by estimates whenever such data is not available or current. Imports are reported on a cost, insurance and freight (CIF) basis and exports are reported on a free on board (FOB) basis, with the exception of a few countries for which imports are also available FOB. Time series data includes estimates derived from reports of partner countries for non-reporting and slow-reporting countries.
Code: DOT
```

#### Find Series Dimensions

In [4]:
```# Look at structure of DOTS data to find the dimensions for our data request
url = "http://dataservices.imf.org/REST/SDMX_JSON.svc/DataStructure/DOT"
dotstruct = requests.get(url).json()
df = pd.DataFrame(dotstruct['Structure']['KeyFamilies']['KeyFamily']\
['Components']['Dimension'])
for x in range(0, 4):
items = ("Dimension", str(x+1), str(df['@codelist'][x]))
print ': '.join(items)
```
```Dimension: 1: CL_FREQ
Dimension: 2: CL_AREA_DOT
Dimension: 3: CL_INDICATOR_DOT
Dimension: 4: CL_COUNTERPART_AREA_DOT```

We can now copy the code for each dimension into the CodeList Method to get the list of possible values. For example, we will need to identify the value of the second dimension, CL_AREA_DOT, for the United States. Below, we show that the code is US. I’ve manually placed the index number for the U.S. and World codes (again to save space), however, you can replace [200, 248] with [0, 248] to get the full list of country/area codes.

#### Find Country Codes

In [5]:
```# Obtain country codes
url = "http://dataservices.imf.org/REST/SDMX_JSON.svc/CodeList/CL_AREA_DOT"
country = requests.get(url).json()
df = pd.DataFrame(country['Structure']['CodeLists']['CodeList']['Code'])
for x in [200, 248]:
items = (str(df['@value'][x]), str(df['Description'][x]['#text']))
print ': '.join(items)
```
```US: United States
W00: All Countries, excluding the IO
```

The series ID is DOT and the country codes (we will use this with the exporting country, CL_AREA_DOT, and the counterpart, CL_COUNTERPART_AREA_DOT) of interest are W00 for world and US for the US. We see below that the indicator of interest is TXG_FOB_USD, Goods, Value of Exports, Free on board (FOB), US Dollars.

#### Find Column IDs

In [6]:
```# Obtain series info and ids
url = "http://dataservices.imf.org/REST/SDMX_JSON.svc/CodeList/CL_INDICATOR_DOT"
series = requests.get(url).json()
df = pd.DataFrame(series['Structure']['CodeLists']['CodeList']['Code'])
for x in range(0, 4):
items = (str(df['@value'][x]), str(df['Description'][x]['#text']))
print ': '.join(items)
```
```TXG_FOB_USD: Goods, Value of Exports, Free on board (FOB), US Dollars
TMG_CIF_USD: Goods, Value of Imports, Cost, Insurance, Freight (CIF), US Dollars
TMG_FOB_USD: Goods, Value of Imports, Free on board (FOB), US Dollars
All Indicators: All Indicators
```

We repeat the above steps for each dimension and record which series values are of interest to us.

### Retrieving Data

The guide to STA’s API shows how we can combine information from the previous steps to call and retrieve data. For direction of trade statistics, we see that the dimensions are as follows:

• Dimension 1: CL_FREQ (the frequency of the data–we want to use monthly data) – M
• Dimension 2: CL_AREA_DOT (the primary country) – US
• Dimension 3: CL_INDICATOR_DOT (the measure–we want to look at exports free of board) – TXG_FOB_USD
• Dimension 4: CL_COUNTERPART_AREA_DOT (the counterpart country) – W00

The JSON RESTful API method for requesting the data is the CompactData Method. The format for putting together dimension and time period information is shown on the Web Service knowledge base as:

```http://dataservices.imf.org/REST/SDMX_JSON.svc/CompactData/{database ID}/ {item1 from dimension1}+{item2 from dimension1}{item N from dimension1}.{item1 from dimension2} +{item2 from dimension2}+{item M from dimension2}? startPeriod={start date}&endPeriod={end date}

```

Putting all of this information together, the URL to retrieve a JSON dictionary for 1966-2016 US exports to the world data is:

http://dataservices.imf.org/REST/SDMX_JSON.svc/CompactData/DOT/M.US.TXG_FOB_USD.W00.?startPeriod=1981&endPeriod=2016

The python code which gets the data and saves it as a dictionary is as follows:

#### Request data from IMF API

In [7]:
```url = 'http://dataservices.imf.org/REST/SDMX_JSON.svc/CompactData/DOT/M.US.TXG_FOB_USD.W00.?startPeriod=1981&endPeriod=2016'
data = requests.get(url).json()
usexp = pd.DataFrame(data['CompactData']['DataSet']['Series']['Obs'])
usexp.columns = ['status', 'usexports','date'];
usexp.tail()
```
Out[7]:
date usexports
415 2015-08 123065777734
416 2015-09 125394024247
417 2015-10 130599515853
418 2015-11 120731632371
419 2015-12 119907169367

We can repeat the above code with a different URL to obtain data on total world exports and the exports of other countries which we may want to compare with the United States. We combine the request for several series into one URL, by adding ‘+code2+code3’. For example, ‘US+JP+CN.TXG..’

#### Example of request with multiple columns

In [8]:
```ourl = 'http://dataservices.imf.org/REST/SDMX_JSON.svc/CompactData/DOT/M.US+CN+JP+W00.TXG_FOB_USD.W00.?startPeriod=1972&endPeriod=2016'
odata = requests.get(ourl).json();
```

#### Cleaning the dataframe and naming rows

In [9]:
```wexp = pd.DataFrame(odata['CompactData']['DataSet']['Series'][0]['Obs'])
wexp.columns = ['status','wexports','date']
del wexp['date']
del wexp['status']
chexp = pd.DataFrame(odata['CompactData']['DataSet']['Series'][1]['Obs'])
chexp.columns = ['status', 'chexports','date']
del chexp['date']
del chexp['status']
jpexp = pd.DataFrame(odata['CompactData']['DataSet']['Series'][2]['Obs'])
jpexp.columns = ['jpexports','date']
del jpexp['date']
usexp = pd.DataFrame(odata['CompactData']['DataSet']['Series'][3]['Obs'])
usexp.columns = ['status', 'usexports','date']
del usexp['status'];
```

Now we combine the two series into one dataframe and tell our script to read the export value columns as numbers.

In [10]:
```combined = pd.concat([usexp, wexp, chexp, jpexp], axis=1)
pd.to_datetime(combined.date)
combined = combined.set_index(pd.DatetimeIndex(combined['date']))
usexports = pd.to_numeric(combined.usexports)
wexports = pd.to_numeric(combined.wexports)
cexports = pd.to_numeric(combined.chexports)
jexports = pd.to_numeric(combined.jpexports)
```

Finally, we can calculate the U.S. percentage share of world exports. We simply divide the us exports by the world exports and multiply by 100. If using the data for economic research, we would likely take the log forms and apply some filters.

#### Calculate share of world exports for each country

In [11]:
```combined['usshare'] = usexports / wexports * 100
combined['chinashare'] = cexports / wexports * 100
combined['japanshare'] = jexports / wexports * 100
combined.tail()
```

Out[11]:

date usshare chinashare japanshare
2015-08 9.460 15.121 3.668
2015-09 8.830 14.455 3.754
2015-10 9.330 13.737 3.892
2015-11 9.018 14.663 3.645
2015-12 8.776 16.362 3.804

### Graphing the data

Let’s use matplotlib to view the result of our work.

#### Graph of US share of world exports

In [12]:
```import matplotlib as mpl
import matplotlib.pyplot as plt
%matplotlib inline
txt = '''Source: International Monetary Fund.'''

# Plot US share of world exports
combined.usshare.plot(grid=True, figsize=(9, 5), color="blue", linewidth=2,)
plt.ylabel('percentage of world exports')
plt.xlabel('Year')
plt.text(20,4.5,txt)
plt.title('U.S. Share of World Exports');
```

The graph shows a decrease in the U.S. share of exports from nearly 20 percent in 1966 to roughly 9 percent in 2015. We can also easily examine how changes in the U.S. share of exports compare with changes in the share of Japan and China.

#### Graph of moving average of US, China, and Japan shares of world exports

In [13]:
```# Calculate moving average for each share, to reduce noise
combined['ussharema'] = combined['usshare'].rolling(12,12).mean()
combined['chsharema'] = combined['chinashare'].rolling(12,12).mean()
combined['jpsharema'] = combined['japanshare'].rolling(12,12).mean()

combshares = combined[['ussharema', 'chsharema', 'jpsharema']]
shares = list(combshares);
# Plot various shares of world exports
combined[shares][120:].plot(grid=True, figsize=(9, 5), linewidth=2)
plt.ylabel('percentage of world exports')
plt.xlabel('Year')
plt.text(150,-2,txt)
plt.title('Share of World Exports', );
```

### Export dataset to .csv

Let’s save the dataset in a portable format that can be read by any statistical software. My preference is to create a .csv file, which I will use for my U.S. Macroeconomic and Markets Dashboard.

#### Create csv file

In [14]:
```combined.to_csv('us_share_exports.csv')
```