Drawing Charts#

This notebook presents various options for drawing charts of data, to complement the Week 3 chart types video.

This tutorial uses concepts from both the Selection and Reshaping notebooks.

This notebook uses the “MovieLens + IMDB/RottenTomatoes” data from the HETREC data. It also uses data sets built in to Seaborn.

Setup#

First we will import our modules:

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt
import seaborn as sns

Then import the HETREC MovieLens data. A few notes:

Tab-separated data
Not UTF-8 - latin-1 encoding seems to work
Missing data encoded as \N (there’s a good chance that what we have is a PostgreSQL data dump!)

Movies#

movies = pd.read_csv('hetrec2011-ml/movies.dat', delimiter='\t', encoding='latin1', na_values=['\\N'])
movies.head()

	id	title	imdbID	spanishTitle	imdbPictureURL	year	rtID	rtAllCriticsRating	rtAllCriticsNumReviews	rtAllCriticsNumFresh	...	rtAllCriticsScore	rtTopCriticsRating	rtTopCriticsNumReviews	rtTopCriticsNumFresh	rtTopCriticsNumRotten	rtTopCriticsScore	rtAudienceRating	rtAudienceNumRatings	rtAudienceScore	rtPictureURL
0	1	Toy story	114709	Toy story (juguetes)	http://ia.media-imdb.com/images/M/MV5BMTMwNDU0...	1995	toy_story	9.0	73.0	73.0	...	100.0	8.5	17.0	17.0	0.0	100.0	3.7	102338.0	81.0	http://content7.flixster.com/movie/10/93/63/10...
1	2	Jumanji	113497	Jumanji	http://ia.media-imdb.com/images/M/MV5BMzM5NjE1...	1995	1068044-jumanji	5.6	28.0	13.0	...	46.0	5.8	5.0	2.0	3.0	40.0	3.2	44587.0	61.0	http://content8.flixster.com/movie/56/79/73/56...
2	3	Grumpy Old Men	107050	Dos viejos gruñones	http://ia.media-imdb.com/images/M/MV5BMTI5MTgy...	1993	grumpy_old_men	5.9	36.0	24.0	...	66.0	7.0	6.0	5.0	1.0	83.0	3.2	10489.0	66.0	http://content6.flixster.com/movie/25/60/25602...
3	4	Waiting to Exhale	114885	Esperando un respiro	http://ia.media-imdb.com/images/M/MV5BMTczMTMy...	1995	waiting_to_exhale	5.6	25.0	14.0	...	56.0	5.5	11.0	5.0	6.0	45.0	3.3	5666.0	79.0	http://content9.flixster.com/movie/10/94/17/10...
4	5	Father of the Bride Part II	113041	Vuelve el padre de la novia (Ahora también abu...	http://ia.media-imdb.com/images/M/MV5BMTg1NDc2...	1995	father_of_the_bride_part_ii	5.3	19.0	9.0	...	47.0	5.4	5.0	1.0	4.0	20.0	3.0	13761.0	64.0	http://content8.flixster.com/movie/25/54/25542...

5 rows × 21 columns

movies.info()

<class 'pandas.core.frame.DataFrame'>
RangeIndex: 10197 entries, 0 to 10196
Data columns (total 21 columns):
 #   Column                  Non-Null Count  Dtype  
---  ------                  --------------  -----  
 id                      10197 non-null  int64  
 title                   10197 non-null  object 
 imdbID                  10197 non-null  int64  
 spanishTitle            10197 non-null  object 
 imdbPictureURL          10016 non-null  object 
 year                    10197 non-null  int64  
 rtID                    9886 non-null   object 
 rtAllCriticsRating      9967 non-null   float64
 rtAllCriticsNumReviews  9967 non-null   float64
 rtAllCriticsNumFresh    9967 non-null   float64
rtAllCriticsNumRotten   9967 non-null   float64
rtAllCriticsScore       9967 non-null   float64
rtTopCriticsRating      9967 non-null   float64
rtTopCriticsNumReviews  9967 non-null   float64
rtTopCriticsNumFresh    9967 non-null   float64
rtTopCriticsNumRotten   9967 non-null   float64
rtTopCriticsScore       9967 non-null   float64
rtAudienceRating        9967 non-null   float64
rtAudienceNumRatings    9967 non-null   float64
rtAudienceScore         9967 non-null   float64
rtPictureURL            9967 non-null   object 
dtypes: float64(13), int64(3), object(5)
memory usage: 1.6+ MB

It’s useful to index movies by ID, so let’s just do that now.

movies = movies.set_index('id')

Movie Info#

movie_genres = pd.read_csv('hetrec2011-ml/movie_genres.dat', delimiter='\t', encoding='latin1')
movie_genres.head()

	movieID	genre
0	1	Adventure
1	1	Animation
2	1	Children
3	1	Comedy
4	1	Fantasy

movie_tags = pd.read_csv('hetrec2011-ml/movie_tags.dat', delimiter='\t', encoding='latin1')
movie_tags.head()

	movieID	tagID	tagWeight
0	1	7	1
1	1	13	3
2	1	25	3
3	1	55	3
4	1	60	1

tags = pd.read_csv('hetrec2011-ml/tags.dat', delimiter='\t', encoding='latin1')
tags.head()

	id	value
0	1	earth
1	2	police
2	3	boxing
3	4	painter
4	5	whale

Ratings#

ratings = pd.read_csv('hetrec2011-ml/user_ratedmovies-timestamps.dat', delimiter='\t', encoding='latin1')
ratings.head()

	userID	movieID	rating	timestamp
0	75	3	1.0	1162160236000
1	75	32	4.5	1162160624000
2	75	110	4.0	1162161008000
3	75	160	2.0	1162160212000
4	75	163	4.0	1162160970000

We’re going to compute movie statistics too:

movie_stats = ratings.groupby('movieID')['rating'].agg(['count', 'mean']).rename(columns={
    'mean': 'MeanRating',
    'count': 'RatingCount'
})
movie_stats.head()

	RatingCount	MeanRating
movieID
1	1263	3.735154
2	765	2.976471
3	252	2.873016
4	45	2.577778
5	225	2.753333

Titanic data#

We’ll also use the Titanic data set from Seaborn:

titanic = sns.load_dataset('titanic')
titanic

	survived	pclass	sex	age	sibsp	parch	fare	embarked	class	who	adult_male	deck	embark_town	alive	alone
0	0	3	male	22.0	1	0	7.2500	S	Third	man	True	NaN	Southampton	no	False
1	1	1	female	38.0	1	0	71.2833	C	First	woman	False	C	Cherbourg	yes	False
2	1	3	female	26.0	0	0	7.9250	S	Third	woman	False	NaN	Southampton	yes	True
3	1	1	female	35.0	1	0	53.1000	S	First	woman	False	C	Southampton	yes	False
4	0	3	male	35.0	0	0	8.0500	S	Third	man	True	NaN	Southampton	no	True
...	...	...	...	...	...	...	...	...	...	...	...	...	...	...	...
886	0	2	male	27.0	0	0	13.0000	S	Second	man	True	NaN	Southampton	no	True
887	1	1	female	19.0	0	0	30.0000	S	First	woman	False	B	Southampton	yes	True
888	0	3	female	NaN	1	2	23.4500	S	Third	woman	False	NaN	Southampton	no	False
889	1	1	male	26.0	0	0	30.0000	C	First	man	True	C	Cherbourg	yes	True
890	0	3	male	32.0	0	0	7.7500	Q	Third	man	True	NaN	Queenstown	no	True

891 rows × 15 columns

Bar Charts#

If we have: a categorical variable and a numeric response variable
And we want: to see how the mean of the numeric varies with the categorical
Then we can: use Seaborn catplot to create a bar chart:

sns.catplot('class', 'survived', data=titanic, kind='bar')

<seaborn.axisgrid.FacetGrid at 0x2c291b61790>

There are quite a few things going on here:

catplot by default computes the mean and 95% bootstrapped confidence intervals.
If we have a 0/1 variable or a logical, such as survived, taking its mean is the same as counting the proportion that are 1 or True; this is also the same as computing the probability of a true value. This is a very useful trick.
Most (but not all) Seaborn plotting functions natively work with data frames; we give column names for the x and y axes, respectively, and provide the data frame as data=, and it plots.
The bars are different colors for no reason. This is annoying.

We can fix that last problem:

sns.catplot('class', 'survived', data=titanic, kind='bar', color='firebrick')

<seaborn.axisgrid.FacetGrid at 0x2c2921d81c0>

But we can also go further.

If we have: two categorical variables and a numeric response variable
And we want: to see how the mean of the numeric varies with the combination of categorical variables
Then we can: use Seaborn catplot to create a bar chart with color-coded bars by mapping a variable to hue:

sns.catplot('class', 'survived', data=titanic, kind='bar', hue='sex')

<seaborn.axisgrid.FacetGrid at 0x2c29225d6d0>

Interlude: Labeling Figures#

Seaborn calls Matplotlib under the hood, so all of Matplotlib’s functions are available to clean up our plot.

Let’s label our axes and give the chart a title:

sns.catplot('class', 'survived', data=titanic, kind='bar', hue='sex')
plt.ylabel('Survival Probability')
plt.xlabel('Passage Class')
plt.title('Survival by Class and Sex')
plt.show()

The plt.show() call tells Matplotlib to show the plot, and returns nothing, which cleans up the notebook display a bit (otherwise we also see the return value of the last plotting function, which is annoying and usually meaningless).

Scatter Plots#

If we have: two numeric variables
And we want: to plot each point in two-dimensional space based on the variable values
Then we can: use a scatter plot.

We saw this in an earlier notebook - let’s look at the relationship of Rotten Tomatoes critic and audience scores:

movie_scores = movies[['year', 'rtAllCriticsRating', 'rtAudienceRating']].rename(columns={
    'rtAllCriticsRating': 'Critics',
    'rtAudienceRating': 'Audience'
})
movie_scores

	year	Critics	Audience
id
1	1995	9.0	3.7
2	1995	5.6	3.2
3	1993	5.9	3.2
4	1995	5.6	3.3
5	1995	5.3	3.0
...	...	...	...
65088	2008	4.4	3.5
65091	1934	7.0	3.7
65126	2008	5.6	3.3
65130	2008	6.7	3.5
65133	1999	0.0	0.0

10197 rows × 3 columns

sns.scatterplot('Critics', 'Audience', data=movie_scores)

<matplotlib.axes._subplots.AxesSubplot at 0x2c2922dd640>

We can see more things, including distributions in the margin, with the more sophisticated jointplot:

sns.jointplot('Critics', 'Audience', data=movie_scores)

<seaborn.axisgrid.JointGrid at 0x2c2923c1550>

Now the top and right margins show the histograms of the those values!

Line Chart#

If we have: two numeric variables, with one that reasonably defines a ‘series’ that they progress along
And we want: to show how variables change from one value of the ‘series’ variable to another
Then we can: use a line chart.

We saw this with the average scores by year previously.

year_scores = movie_scores.groupby('year').mean()
ys_tall = year_scores.reset_index().melt(id_vars='year', var_name='Source', value_name='MeanAvgScore')
ys_tall

	year	Source	MeanAvgScore
0	1903	Critics	7.600000
1	1915	Critics	8.000000
2	1916	Critics	7.800000
3	1917	Critics	0.000000
4	1918	Critics	0.000000
...	...	...	...
191	2007	Audience	3.062162
192	2008	Audience	2.853698
193	2009	Audience	3.192308
194	2010	Audience	0.000000
195	2011	Audience	0.000000

196 rows × 3 columns

sns.lineplot('year', 'MeanAvgScore', hue='Source', data=ys_tall)

<matplotlib.axes._subplots.AxesSubplot at 0x2c29250e640>

*Practice: add the mean average rating from MovieLens users to this chart.

Box Plots#

These show median-based distribution statistics for a numeric variable grouped by a categorical.

If we have: a numeric response variable and a categorical variable
And we want: to visualize median-based distribution statistics (min, max, IQR)
Then we can: use a box plot.

Let’s look at the distribution of rating counts by genre. We first need to join genres and movie stats.

mg_stats = movie_genres.join(movie_stats, on='movieID')
mg_stats

	movieID	genre	RatingCount	MeanRating
0	1	Adventure	1263.0	3.735154
1	1	Animation	1263.0	3.735154
2	1	Children	1263.0	3.735154
3	1	Comedy	1263.0	3.735154
4	1	Fantasy	1263.0	3.735154
...	...	...	...	...
20804	65126	Comedy	2.0	3.250000
20805	65126	Drama	2.0	3.250000
20806	65130	Drama	1.0	2.500000
20807	65130	Romance	1.0	2.500000
20808	65133	Comedy	3.0	4.000000

20809 rows × 4 columns

sns.boxplot('RatingCount', 'genre', data=mg_stats)

<matplotlib.axes._subplots.AxesSubplot at 0x2c2925842e0>

Note that this is horizontal rather than vertical - Seaborn automatically figures out which is numeric and which is categorical, and orients the box plot correctly. Horizontal is easier to have good layouts for the y axis labels.

Violin Plots#

The violin plot also shows distributions, but does so with a kernel density estimate:

sns.violinplot('MeanRating', 'genre', data=mg_stats)

<matplotlib.axes._subplots.AxesSubplot at 0x2c2923417c0>

This chart is too crowded to usefully read.

Wrapping Up#

The Seaborn functions have a common interface:

x and y as first and second parameters, respectively
if data= points to a data frame, then x and y are interpreted as column names
can change other aesthetics, such as color-coding points with hue='column'

We’ll see more plot capabilities later.

CS 533 Fall 2022

Drawing Charts

Contents