<SYSTEM_TASK:>
Given the following text description, write Python code to implement the functionality described below step by step
<END_TASK>
<USER_TASK:>
Description:
 Python graphics
Step1:  Comment.  When you run the code cell above, its output appears below it.  
Exercise. Enter pd.read_csv? in the empty cell below.  Run the cell (Cell at the top, or shift-enter).  Do you see the documentation?  This is the Jupyter version of help in Spyder's IPython console.
Step2:  Create dataframes to play with
US GDP and consumption 
World Bank GDP per capita for several countries 
Fama-French equity returns
Step3:  Comment.  In the previous cell, we used the print() function to produce output.  Here we just put the name of the dataframe.  The latter displays the dataframe -- and formats it nicely -- if it's the last statement in the cell.
Step4:  Comment.  The warning in pink tells us that the Pandas DataReader will be spun off into a separate package in the near future.  
Exercise. What kind of object is wbdf?  What are its column and row labels?  
Exercise. What is ff.index?  What does that tell us?
Step5:  Digression
Step6:  Exercise. Show that we get the output from us.plot.bar().
Step7:  Exercise. Enter us.plot(kind='bar') and us.plot.bar() in separate cells.  Show that they produce the same bar chart.  
Exercise.  Add each of these arguments, one at a time, to us.plot()
Step8:  Exercise. What do each of the arguments do in the code below?
Step9:  Exercise.  Let's see if we can dress up the histogram a little.  Try adding, one at a time, the arguments title='Fama-French returns', grid=True, and legend=False.  What does the documentation say about them?  What do they do?  
Exercise.  What do the histograms tell us about the two returns?  How do they differ?  
Exercise.  Use the World Bank dataframe wbdf to create a bar chart of GDP per capita, the variable 'gdppc'. Bonus points
Step10:  Exercise. What is the x variable here?  The y variable?
Step11:  Exercise. Experiment with 
python
plt.bar(us.index, us['gdp'], 
        align='center', 
        alpha=0.65, 
        color='red', 
        edgecolor='green')
Play with the arguments one by one to see what they do.  Or use plt.bar? to look them up.  Add comments to remind yourself. Bonus points
Step12:  Comment. All of these statements must be in the same cell for this to work.  
Comment. This is overkill -- it looks horrible -- but it makes the point that we control everything in the plot.  We recommend you do very little of this until you're more comfortable with the basics.  
Exercise. Add a plt.ylim() statement to make the y axis start at zero, as it did in the bar charts.  Bonus points
Step13:  Exercise. What do we have here?  What type are fig and ax?  
We say fig is a figure object and ax is an axis object.  This means
Step14:  Comment. Both of these statements must be in the same cell.
Step15:  Exercise.  Let's see if we can teach ourselves the rest
Step16:  (Your results may differ, but we really enjoyed that.) 
Exercise. Use the set_xlabel() method to add an x-axis label.  What would you choose?  Or would you prefer to leave it empty?  
Exercise. Enter ax.set_legend? to access the documentation for the set_legend method.  What options appeal to you?  
Exercise.  Change the line width to 2 and the line colors to blue and magenta.  Hint
Step17:  Examples
We conclude with examples that take the data from the previous chapter and make better graphs with it.  
Student test scores (PISA)
The international test scores often used to compare quality of education across countries.
Step18:  Comment. Yikes!  That's horrible!  What can we do about it?  
Let's make the figure taller.  The figsize argument has the form (width, height).  The default is (6, 4).  We want a tall figure, so we need to increase the height setting.
Step19:  Comment. What if we wanted to make the US bar red?  This is ridiculously complicated, but we used our Google fu and found a solution.  Remember
Step20:  Exercise. Create the same graph for the Reading score.  
World Bank data
We'll use World Bank data for GDP, GDP per capita, and life expectancy to produce a few graphs and illsutrate some methods we haven't seen yet.   
Bar charts of GDP and GDP per capita 
Scatter plot (bubble plot) of life expectancy v GDP per capita
Step21:  And just because it's fun, here's an example of Tufte-like axes from Matplotlib examples.  If you want to do this yourself, copy the last six line and prepare yourself to sink some time into it.
Step22:  Exercise (challenging).  Make the ticks point out.
Step23:  Exercise. Make the bubble a little larger.  
Styles (optional)
Graph settings you might like.
Step24:  Exercise.  Create the same graph with this statement at the top
Step25:  Comment. Ignore the seaborn styles, that's a package we don't have yet.  
Exercise. Try another one by editing the code below.
Step26:  Comment. For aficionados, the always tasteful xkcd style.
Step27:  Comment. We reset the style with these two lines
<ASSISTANT_TASK:>
Python Code:
import sys                             # system module 
import pandas as pd                    # data package
import matplotlib as mpl               # graphics package
import matplotlib.pyplot as plt        # graphics module  
import datetime as dt                  # date and time module
# check versions (overkill, but why not?)
print('Python version:', sys.version)
print('Pandas version: ', pd.__version__)
print('Matplotlib version: ', mpl.__version__)
print('Today: ', dt.date.today())
Explanation: Python graphics:  Matplotlib fundamentals
We illustrate three approaches to graphing data with Python's Matplotlib package:    
Approach #1:  Apply a plot() method to a dataframe
Approach #2:  Use the plot(x,y) function 
Approach #3:  Create a figure object and apply methods to it
The last one is the least intuitive but also the most useful.  We work up to it gradually.  This book chapter covers the same material with more words and fewer pictures.  
This IPython notebook was created by Dave Backus for the NYU Stern course Data Bootcamp.  
Reminders
Packages:  collections of tools that we access with import statements
Pandas:  Python's data package 
Objects and methods:  we apply the method justdoit to the object x with x.justdoit
Dataframe:  a spreadsheet-like data structure 
Series:  a single variable 
Jupyter:  an environment for combining code with text and graphics 
Preliminaries
Jupyter
Look around, what do you see?  Check out the menubar at the top:  File, Edit, etc.  Also the toolbar below it.  Click on Help -> User Interface Tour for a tour of the landscape.  
The cells below come in two forms.  Those labeled Code (see the menu in the toolbar) are Python code.  Those labeled Markdown are text.  
Markdown
Markdown is a user-friendly language for text formatting.  You can see how it works by clicking on any of the Markdown cells and looking at the raw text that underlies it. In addition to just plain text, we'll use three things a lot:
Bold and italics.  The raw text **bold** displays as bold.  The raw text *italics* displays as italics.  
Bullet lists.  If we want a list of items marked by bullets, we start with a blank line and mark each item with an asterisk on a new line.  Double click on this cell for an example.   
Headings.  We create section headings by putting a hash in front of the text.  # Heading gives us a large heading.  Two hashes a smaller heading, three hashes smaller still, up to four hashes.  In this cell there's a two-hash heading at the top.  
Exercise. Click on this cell, then click the + in the toolbar to create a new empty cell below.  
Exercise. Click on the new cell below.  Choose Markdown in the menubar at the top.  Add your name and a description of what we're doing. Execute the cell by either (i) clicking on the "run cell" button in the toolbar or (ii) clicking on "Cell" in the menubar and choosing Run. 
Import packages
End of explanation
# This is an IPython command.  It puts plots here in the notebook, rather than a separate window.
%matplotlib inline
Explanation: Comment.  When you run the code cell above, its output appears below it.  
Exercise. Enter pd.read_csv? in the empty cell below.  Run the cell (Cell at the top, or shift-enter).  Do you see the documentation?  This is the Jupyter version of help in Spyder's IPython console.
End of explanation
# US GDP and consumption 
gdp  = [13271.1, 13773.5, 14234.2, 14613.8, 14873.7, 14830.4, 14418.7,
        14783.8, 15020.6, 15369.2, 15710.3]
pce  = [8867.6, 9208.2, 9531.8, 9821.7, 10041.6, 10007.2, 9847.0, 10036.3,
        10263.5, 10449.7, 10699.7]
year = list(range(2003,2014))        # use range for years 2003-2013 
# create dataframe from dictionary 
us = pd.DataFrame({'gdp': gdp, 'pce': pce}, index=year) 
print(us.head(3))
# GDP per capita (World Bank data, 2013, thousands of USD) 
code    = ['USA', 'FRA', 'JPN', 'CHN', 'IND', 'BRA', 'MEX']
country = ['United States', 'France', 'Japan', 'China', 'India',
             'Brazil', 'Mexico']
gdppc   = [53.1, 36.9, 36.3, 11.9, 5.4, 15.0, 16.5]
wbdf = pd.DataFrame({'gdppc': gdppc, 'country': country}, index=code)
wbdf
Explanation: Create dataframes to play with
US GDP and consumption 
World Bank GDP per capita for several countries 
Fama-French equity returns
End of explanation
# Fama-French 
import pandas.io.data as web
# read annual data from website and rename variables 
ff = web.DataReader('F-F_Research_Data_factors', 'famafrench')[1]
ff.columns = ['xsm', 'smb', 'hml', 'rf']
ff['rm'] = ff['xsm'] + ff['rf']
ff = ff[['rm', 'rf']]     # extract rm and rf (return on market, riskfree rate, percent)
ff.head(5)
Explanation: Comment.  In the previous cell, we used the print() function to produce output.  Here we just put the name of the dataframe.  The latter displays the dataframe -- and formats it nicely -- if it's the last statement in the cell.
End of explanation
# This is an IPython command:  it puts plots here in the notebook, rather than a separate window.
%matplotlib inline
Explanation: Comment.  The warning in pink tells us that the Pandas DataReader will be spun off into a separate package in the near future.  
Exercise. What kind of object is wbdf?  What are its column and row labels?  
Exercise. What is ff.index?  What does that tell us?
End of explanation
# try this with US GDP
us.plot()
# do GDP alone
us['gdp'].plot()
# bar chart 
us.plot(kind='bar')
Explanation: Digression:   Graphing in Excel
Remind yourself that we need to choose:  
Data.  Typically a block of cells in a spreadsheet.  
Chart type.  Lines, bars, scatter, or something else.  
x and y variables.  What is the x axis?  What is y?  
We'll see the same in Matplotlib. 
Approach #1:  Apply plot() method to dataframe
Good simple approach, we use it a lot.  It comes with some useful defaults:
Data.  The whole dataframe.  
Chart type.  We have options for lines, bars, or other things.  
x and y variables.  By default, the x variable is the dataframe's index and the y variables are all the columns of the dataframe.  
All of these things can be changed, but this is the starting point.  
Let's do some examples, see how they work. 
US GDP and consumption
End of explanation
us.plot
# scatter plot 
# we need to be explicit about the x and y variables: x = 'gdp', y = 'pce'
us.plot.scatter('gdp', 'pce')
Explanation: Exercise. Show that we get the output from us.plot.bar().
End of explanation
# now try a few things with the Fama-French data
ff.plot()
ff.plot()
Explanation: Exercise. Enter us.plot(kind='bar') and us.plot.bar() in separate cells.  Show that they produce the same bar chart.  
Exercise.  Add each of these arguments, one at a time, to us.plot():  
kind='area'
subplots=True
sharey=True
figsize=(3,6)
ylim=(0,16000)
What do they do?
Exercise. Type us.plot? in a new cell.  Run the cell (shift-enter or click on the run cell icon).  What options do you see for the kind= argument?  Which ones have we tried?  What are the other ones?  
Fama-French asset returns
End of explanation
ff.plot(kind='hist', bins=20, subplots=True)
# "smoothed" histogram 
ff.plot(kind='kde', subplots=True, sharex=True)    # smoothed histogram ("kernel density estimate")
Explanation: Exercise. What do each of the arguments do in the code below?
End of explanation
# import pyplot module of Matplotlib 
import matplotlib.pyplot as plt      
plt.plot(us.index, us['gdp'])
Explanation: Exercise.  Let's see if we can dress up the histogram a little.  Try adding, one at a time, the arguments title='Fama-French returns', grid=True, and legend=False.  What does the documentation say about them?  What do they do?  
Exercise.  What do the histograms tell us about the two returns?  How do they differ?  
Exercise.  Use the World Bank dataframe wbdf to create a bar chart of GDP per capita, the variable 'gdppc'. Bonus points: Create a horizontal bar chart. Which do you prefer?  
Approach #2:  the plot(x,y) function
Here we plot variable y against variable x.  This comes closest to what we would do in Excel:  identify a dataset, a plot type, and the x and y variables, then press play.
End of explanation
# we can do two lines together
plt.plot(us.index, us['gdp'])
plt.plot(us.index, us['pce'])
# or a bar chart 
plt.bar(us.index, us['gdp'], align='center')
Explanation: Exercise. What is the x variable here?  The y variable?
End of explanation
# we can also add things to plots 
plt.plot(us.index, us['gdp']) 
plt.plot(us.index, us['pce']) 
plt.title('US GDP', fontsize=14, loc='left') # add title
plt.ylabel('Billions of 2009 USD')           # y axis label 
plt.xlim(2002.5, 2013.5)                     # shrink x axis limits
plt.tick_params(labelcolor='red')            # change tick labels to red
plt.legend(['GDP', 'Consumption'])           # more descriptive variable names
Explanation: Exercise. Experiment with 
python
plt.bar(us.index, us['gdp'], 
        align='center', 
        alpha=0.65, 
        color='red', 
        edgecolor='green')
Play with the arguments one by one to see what they do.  Or use plt.bar? to look them up.  Add comments to remind yourself. Bonus points:  Can you make this graph even uglier?
End of explanation
# create fig and ax objects
fig, ax = plt.subplots()
Explanation: Comment. All of these statements must be in the same cell for this to work.  
Comment. This is overkill -- it looks horrible -- but it makes the point that we control everything in the plot.  We recommend you do very little of this until you're more comfortable with the basics.  
Exercise. Add a plt.ylim() statement to make the y axis start at zero, as it did in the bar charts.  Bonus points:  Change the color to magenta and the linewidth to 2.  Hint:  Use plt.ylim? and plt.plot? to get the documentation.  
Exercise. Create a line plot for the Fama-French dataframe ff that includes both returns.  Bonus points: Add a title and label the y axis.  
Approach #3:  Create figure objects and apply methods
This approach is the most foreign to beginners, but now that we’re used to it we like it a lot. The idea is to generate an object – two objects, in fact – and apply methods to them to produce the various elements of a graph: the data, their axes, their labels, and so on.
End of explanation
# let's try that again, this time with content  
# create objects 
fig, axe = plt.subplots()
# add things by applying methods to ax 
us.plot(ax=axe) 
Explanation: Exercise. What do we have here?  What type are fig and ax?  
We say fig is a figure object and ax is an axis object.  This means:
fig is a blank canvas for creating a figure.
ax is everything in it:  axes, labels, lines or bars, and so on.  
Exercise. Use tab completion to see what methods are available for fig and ax.  What do you see?  Do you feel like screaming?
End of explanation
# Fama-French example 
fig, ax = plt.subplots()
ff.plot(ax=ax, 
        kind='line',                 # line plot 
        color=['blue', 'magenta'],   # line color 
        title='Fama-French market and riskfree returns')
Explanation: Comment. Both of these statements must be in the same cell.
End of explanation
fig, ax = plt.subplots()
us.plot(ax=ax)       
ax.set_title('US GDP and Consumption', fontsize=14, loc='left')
ax.set_ylabel('Billions of 2013 USD')
ax.legend(['Real GDP', 'Consumption'], loc=0)  # more descriptive variable names 
ax.set_xlim(2002.5, 2013.5)                    # expand x axis limits
ax.tick_params(labelcolor='red')               # change tick labels to red
ax.set_ylim(0)
Explanation: Exercise.  Let's see if we can teach ourselves the rest:  
Add the argument kind='bar' to convert this into a bar chart.  
Add the argument alpha=0.65 to the bar chart.  What does it do?  
What would you change in the bar chart to make it look better?  Use the help facility to find options that might help.  Which ones appeal to you?  
Exercise (somewhat challenging). Use the same approach to reproduce our earlier histograms of the Fama-French series.  
Quick review of the bidding
Take a deep breath.  We've covered a lot of ground, let's take stock.  
We looked at three ways to use Matplotlib:
Approach #1:  apply plot method to dataframe
Approach #2:  use plot(x,y) function 
Approach #3:  create fig, ax objects, apply plot methods to them
Same result, different syntax.  This is what each of them looks like applied to US GDP: 
```python
us['gdp'].plot()                   # Approach #1
plt.plot(us.index, us['gdp'])      # Approach #2
fig, ax = plt.subplots()           # Approach #3 
ax.plot(us.index, us['gdp'])     
```
Bells and whistles
Adding things to graphs
We have lots of choices.  Here's an example.
End of explanation
# this creates a 2-dimensional ax 
fig, ax = plt.subplots(nrows=2, ncols=1, sharex=True)   
print('Object ax has dimension', len(ax))
# now add some content 
fig, ax = plt.subplots(nrows=2, ncols=1, sharex=True, sharey=True)
us['gdp'].plot(ax=ax[0], color='green')   # first plot
us['pce'].plot(ax=ax[1], color='red')     # second plot
Explanation: (Your results may differ, but we really enjoyed that.) 
Exercise. Use the set_xlabel() method to add an x-axis label.  What would you choose?  Or would you prefer to leave it empty?  
Exercise. Enter ax.set_legend? to access the documentation for the set_legend method.  What options appeal to you?  
Exercise.  Change the line width to 2 and the line colors to blue and magenta.  Hint:  Use us.plot? to get the documentation.  
Exercise (challenging). Use the set_ylim() method to start the y axis at zero.  Hint:  Use ax.set_ylim? to get the documentation.  
Exercise. Create a line plot for the Fama-French dataframe ff that includes both returns.  Bonus points: Add a title with the set_title method.  
Multiple subplots
Same idea, but we create a multidimensional ax and apply methods to each component. Here we redo the plots of US GDP and consumption.
End of explanation
# data input 
import pandas as pd
url = 'http://dx.doi.org/10.1787/888932937035'
pisa = pd.read_excel(url, 
                     skiprows=18,     # skip the first 18 rows 
                     skipfooter=7,    # skip the last 7 
                     parse_cols=[0,1,9,13], # select columns 
                     index_col=0,     # set index = first column
                     header=[0,1]     # set variable names 
                     )
pisa = pisa.dropna()                          # drop blank lines 
pisa.columns = ['Math', 'Reading', 'Science'] # simplify variable names 
# bar chart of math scores 
fig, ax = plt.subplots()
pisa['Math'].plot(kind='barh', ax=ax)  
Explanation: Examples
We conclude with examples that take the data from the previous chapter and make better graphs with it.  
Student test scores (PISA)
The international test scores often used to compare quality of education across countries.
End of explanation
fig.
# make the plot taller 
fig, ax = plt.subplots(figsize=(4, 13))  # note figsize 
pisa['Math'].plot(kind='barh', ax=ax)  
ax.set_title('PISA Math Score', loc='left')
Explanation: Comment. Yikes!  That's horrible!  What can we do about it?  
Let's make the figure taller.  The figsize argument has the form (width, height).  The default is (6, 4).  We want a tall figure, so we need to increase the height setting.
End of explanation
fig, ax = plt.subplots()
pisa['Math'].plot(kind='barh', ax=ax, figsize=(4,13))
ax.set_title('PISA Math Score', loc='left')
ax.get_children()[36].set_color('r')
Explanation: Comment. What if we wanted to make the US bar red?  This is ridiculously complicated, but we used our Google fu and found a solution.  Remember: The solution to many problems is Google fu + patience.
End of explanation
# load packages (redundancy is ok)
import pandas as pd                   # data management tools
from pandas.io import wb              # World Bank api
import matplotlib.pyplot as plt       # plotting tools
# variable list (GDP, GDP per capita, life expectancy)
var = ['NY.GDP.PCAP.PP.KD', 'NY.GDP.MKTP.PP.KD', 'SP.DYN.LE00.IN']  
# country list (ISO codes)
iso = ['USA', 'FRA', 'JPN', 'CHN', 'IND', 'BRA', 'MEX']
year = 2013
# get data from World Bank 
df = wb.download(indicator=var, country=iso, start=year, end=year)
# massage data
df = df.reset_index(level='year', drop=True)
df.columns = ['gdppc', 'gdp', 'life'] # rename variables
df['pop']  = df['gdp']/df['gdppc']    # population 
df['gdp'] = df['gdp']/10**12          # convert to trillions
df['gdppc'] = df['gdppc']/10**3       # convert to thousands
df['order'] = [5, 3, 1, 4, 2, 6, 0]   # reorder countries
df = df.sort_values(by='order', ascending=False)
df
# GDP bar chart
fig, ax = plt.subplots()
df['gdp'].plot(ax=ax, kind='barh', alpha=0.5)
ax.set_title('GDP', loc='left', fontsize=14)
ax.set_xlabel('Trillions of US Dollars')
ax.set_ylabel('')
# ditto for GDP per capita (per person)
fig, ax = plt.subplots()
df['gdppc'].plot(ax=ax, kind='barh', color='m', alpha=0.50)  # 'm' == 'magenta'
ax.set_title('GDP Per Capita', loc='left', fontsize=14)
ax.set_xlabel('Thousands of US Dollars')
ax.set_ylabel('')
Explanation: Exercise. Create the same graph for the Reading score.  
World Bank data
We'll use World Bank data for GDP, GDP per capita, and life expectancy to produce a few graphs and illsutrate some methods we haven't seen yet.   
Bar charts of GDP and GDP per capita 
Scatter plot (bubble plot) of life expectancy v GDP per capita
End of explanation
# ditto for GDP per capita (per person)
fig, ax = plt.subplots()
df['gdppc'].plot(ax=ax, kind='barh', color='b', alpha=0.5)
ax.set_title('GDP Per Capita', loc='left', fontsize=14)
ax.set_xlabel('Thousands of US Dollars')
ax.set_ylabel('')
# Tufte-like axes
ax.spines['left'].set_position(('outward', 7))
ax.spines['bottom'].set_position(('outward', 7))
ax.spines['right'].set_visible(False)
ax.spines['top'].set_visible(False)
ax.yaxis.set_ticks_position('left')
ax.xaxis.set_ticks_position('bottom')
Explanation: And just because it's fun, here's an example of Tufte-like axes from Matplotlib examples.  If you want to do this yourself, copy the last six line and prepare yourself to sink some time into it.
End of explanation
# scatterplot of life expectancy vs gdp per capita
fig, ax = plt.subplots()
ax.scatter(df['gdppc'], df['life'],     # x,y variables
            s=df['pop']/10**6,          # size of bubbles
            alpha=0.5)   
ax.set_title('Life expectancy vs. GDP per capita', loc='left', fontsize=14)
ax.set_xlabel('GDP Per Capita')
ax.set_ylabel('Life Expectancy')
ax.text(58, 66, 'Bubble size represents population', horizontalalignment='right')
Explanation: Exercise (challenging).  Make the ticks point out.
End of explanation
# We'll look at this chart under a variety of styles.
# Let's make a function so we don't have to repeat the
# code to create 
def gdp_bar():
    fig, ax = plt.subplots()
    df['gdp'].plot(ax=ax, kind='barh', alpha=0.5)
    ax.set_title('Real GDP', loc='left', fontsize=14)
    ax.set_xlabel('Trillions of US Dollars')
    ax.set_ylabel('')
    
gdp_bar()
Explanation: Exercise. Make the bubble a little larger.  
Styles (optional)
Graph settings you might like.
End of explanation
plt.style.available
Explanation: Exercise.  Create the same graph with this statement at the top:
python
plt.style.use('fivethirtyeight')
(Once we execute this statement, it stays executed.) 
Comment. We can get a list of files from plt.style.available.
End of explanation
plt.style.use('fivethirtyeight')
gdp_bar()
Explanation: Comment. Ignore the seaborn styles, that's a package we don't have yet.  
Exercise. Try another one by editing the code below.
End of explanation
plt.style.use('ggplot')
gdp_bar()
plt.xkcd()
gdp_bar()
Explanation: Comment. For aficionados, the always tasteful xkcd style.
End of explanation
mpl.rcParams.update(mpl.rcParamsDefault)
%matplotlib inline
Explanation: Comment. We reset the style with these two lines:
End of explanation
<END_TASK>