What’s better than a lazy sunday afternoon at my parents’ place, where to hack away a few hours?

Lately joyplots have been all the rage on the nerd part of twitter, thanks to the awesome ggjoy package for R. Joyplots are essentially just a number of stacked overlapping density plots, that look like a mountain ridge, if done right.

I find them usually nice.. and I like the name, that, in case you’re wondering, comes from the art cover of a post-punk masterpiece of the late 70’s, “Unkown Pleasure” by Joy Division.

So I wrote some code to have decent-looking joyplot in python, especially from dataframes. The result is here. I had fun.

Here are some examples.

import joypy
import pandas as pd
from matplotlib import pyplot as plt
from matplotlib import cm

Obligatory iris stuff

Though not a great fit for this kind of visualization, we can generate some joyplots with the iris dataset.

iris = pd.read_csv("data/iris.csv")

By default, joypy.joyplot() will draw joyplot with a density subplot for each numeric column in the dataframe. The density is obtained with the gaussian_kde function of scipy.

%matplotlib inline
fig, axes = joypy.joyplot(iris)

If you pass a grouped dataframe, or if you pass a column name to the by argument, you get a density plot for each value in the grouped column.

%matplotlib inline
fig, axes = joypy.joyplot(iris, by="Name")

In the previous plot, one subplot had a much larger y extensions than the others. Since, by default, the subplots share the y-limits, the outlier causes all the other subplots to be quite compressed.

We can change this behavior letting each subplot take up the whole y space with ylim='own', as follows.

%matplotlib inline
fig, axes = joypy.joyplot(iris, by="Name", ylim='own')

In this case, we achieved more overlap, but the subplots are no longer directly comparable.

Yet another option is to keep the default ylim behavior (i.e., ylim='max'), and simply increase the overlap factor:

%matplotlib inline
fig, axes = joypy.joyplot(iris, by="Name", overlap=3)

It’s also possible to draw histograms with hist=True, though they don’t look nice when overlapping, so it’s better to set overlap=0.

With grid=True or grid='both' you also get grid lines on both axis.

%matplotlib inline
fig, axes = joypy.joyplot(iris, by="Name", column="SepalWidth",
                          hist="True", bins=20, overlap=0,
                          grid=True, legend=False)

Global daily temperatures

Something that is probably a better fit for joyplots than iris: let’s visualize the distribution of global daily temperatures from 1880 to 2014.

(The original file can be found here)

%matplotlib inline

temp = pd.read_csv("data/daily_temp.csv",comment="%")
Date Number Year Month Day Day of Year Anomaly
0 1880.001 1880 1 1 1 -0.808
1 1880.004 1880 1 2 2 -0.670
2 1880.007 1880 1 3 3 -0.740
3 1880.010 1880 1 4 4 -0.705
4 1880.012 1880 1 5 5 -0.752

The column Anomaly contains the global daily temperature (in °C) computed as the difference between the daily value and the 1950-1980 global average. We can draw the distribution of the temperatures in time, grouping by Year, to see how the daily temperature distribution shifted across time.

Since the y label would get pretty crammed if we were to show all the year labels, we first prepare a list where we leave only the multiples of 10.

To reduce the clutter, the option range_style='own' limits the x range of each individual density plot to the range where the density is non-zero (+ an “aestethic” tolerance to avoid cutting the tails too early/abruptly), rather than spanning the whole x axis.

The option colormap=cm.autumn_r provides a colormap to use along the plot.

(Grouping the dataframe and computing the density plots can take a few seconds here.)

%matplotlib inline

labels=[y if y%10==0 else None for y in list(temp.Year.unique())]
fig, axes = joypy.joyplot(temp, by="Year", column="Anomaly", labels=labels, range_style='own', 
                          grid="y", linewidth=1, legend=False, figsize=(6,5),
                          title="Global daily temperature 1880-2014 \n(°C above 1950-80 average)",

If you want, you can also plot the raw counts, rather than the estimated density. This makes for noisier plots, but it might be preferable in some cases.

With fade=True, the subplots get a progressively larger alpha value.

%matplotlib inline

labels=[y if y%10==0 else None for y in list(temp.Year.unique())]
fig, axes = joypy.joyplot(temp, by="Year", column="Anomaly", labels=labels, range_style='own', 
                          grid="y", linewidth=1, legend=False, fade=True, figsize=(6,5),
                          title="Global daily temperature 1880-2014 \n(°C above 1950-80 average)",
                          kind="counts", bins=30)

Just for fun, let’s plot the same data as it were on the cover of Unknown Pleasures, the Joy Division’s album where the nickname to this kind of visualization comes from.

No labels/grids, no filling, black background, white lines, and a couple of adjustments just to make it look a bit more like the album cover.

%matplotlib inline

fig, axes = joypy.joyplot(temp,by="Year", column="Anomaly", ylabels=False, xlabels=False, 
                          grid=False, fill=False, background='k', linecolor="w", linewidth=1,
                          legend=False, overlap=0.5, figsize=(6,5),kind="counts", bins=80)

plt.subplots_adjust(left=0, right=1, top=1, bottom=0)
for a in axes[:-1]:

NBA players - regular season stats

The files can be obtained from Kaggle datasets.

players = pd.read_csv("data/Players.csv",index_col=0)
Player height weight collage born birth_city birth_state
0 Curly Armstrong 180.0 77.0 Indiana University 1918.0 NaN NaN
1 Cliff Barker 188.0 83.0 University of Kentucky 1921.0 Yorktown Indiana
2 Leo Barnhorst 193.0 86.0 University of Notre Dame 1924.0 NaN NaN
3 Ed Bartels 196.0 88.0 North Carolina State University 1925.0 NaN NaN
4 Ralph Beard 178.0 79.0 University of Kentucky 1927.0 Hardinsburg Kentucky
seasons = pd.read_csv("data/Seasons_Stats.csv", index_col=0)
0 1950.0 Curly Armstrong G-F 31.0 FTW 63.0 NaN NaN NaN 0.368 ... 0.705 NaN NaN NaN 176.0 NaN NaN NaN 217.0 458.0
1 1950.0 Cliff Barker SG 29.0 INO 49.0 NaN NaN NaN 0.435 ... 0.708 NaN NaN NaN 109.0 NaN NaN NaN 99.0 279.0
2 1950.0 Leo Barnhorst SF 25.0 CHS 67.0 NaN NaN NaN 0.394 ... 0.698 NaN NaN NaN 140.0 NaN NaN NaN 192.0 438.0
3 1950.0 Ed Bartels F 24.0 TOT 15.0 NaN NaN NaN 0.312 ... 0.559 NaN NaN NaN 20.0 NaN NaN NaN 29.0 63.0
4 1950.0 Ed Bartels F 24.0 DNN 13.0 NaN NaN NaN 0.308 ... 0.548 NaN NaN NaN 20.0 NaN NaN NaN 27.0 59.0

5 rows × 52 columns

Join the dataframes and filter:

  • years starting from the 3 point line introduction (1979-80)
  • player seasons with at least 10 field goal attempts.
joined = seasons.merge(players, on="Player")
threepoints = joined[(joined.Year >= 1979) & (joined["FGA"] > 10)].sort_values("Year")
threepoints["3Pfract"] = threepoints["3PA"]/threepoints.FGA

The fraction of 3 pointers attempted by each player in a season has clearly shifted a lot.
In today’s NBA there’s a good number of players who take 40% or more of their shots from behind the line.

%matplotlib inline

decades = [int(y) if y%10==0 or y == 2017 else None for y in threepoints.Year.unique()]
fig, axes = joypy.joyplot(threepoints, by="Year", column="3Pfract",
                  range_style='own', tails=0.2, 
                  overlap=3, linewidth=1, colormap=cm.autumn_r,
                  labels=decades, grid='y', figsize=(7,7), 
                  title="Fraction of 3 pointers \n over all field goal attempts")#, x_range=[-0.05,1])

In this last plot, the distributions of the 3P percentages across the players are drawn as raw binned counts.

With kind=normalized_counts, the values are normalized over the occurrences in each year: this is probably needed here, because that the number of teams and players in the NBA has grown during the years.

The median NBA player has become a much better 3P shooter: no big surprise there!

%matplotlib inline

threepoint_shooters = threepoints[threepoints["3PA"] >= 20] 
decades = [int(y) if y%10==0 or y == 2017 else None for y in threepoint_shooters.Year.unique()]
fig, axes = joypy.joyplot(threepoint_shooters, by="Year", column="3P%",
                   kind="normalized_counts", bins=30, 
                   range_style='all', x_range=[-0.05,0.65],
                   overlap=2, linewidth=1, colormap=cm.autumn_r,
                   labels=decades, grid='both', figsize=(7,7),
                   title="3 Points % \n(at least 20 3P attempts)")