#125 Small multiples for line chart

Let’s say you want to realise a line chart with several lines, one for each group of your dataset. Adding all of them on the same plot can quickly lead to a spaghetti plot, and thus provide a chart that is hard to read and gives few insight about the data.

Several ways exist to avoid it, and one of them consists to use small multiple: here we cut the window in several subplots, one per group. Then, you can choose to display discreetly every groups, or not showing them at all. Note that you can easily do the same with area chart.

Left graph

# libraries and data
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd

# Make a data frame
df=pd.DataFrame({'x': range(1,11), 'y1': np.random.randn(10), 'y2': np.random.randn(10)+range(1,11), 'y3': np.random.randn(10)+range(11,21), 'y4': np.random.randn(10)+range(6,16), 'y5': np.random.randn(10)+range(4,14)+(0,0,0,0,0,0,0,-3,-8,-6), 'y6': np.random.randn(10)+range(2,12), 'y7': np.random.randn(10)+range(5,15), 'y8': np.random.randn(10)+range(4,14), 'y9': np.random.randn(10)+range(4,14) })

# Initialize the figure
plt.style.use('seaborn-darkgrid')

# create a color palette
palette = plt.get_cmap('Set1')

# multiple line plot
num=0
for column in df.drop('x', axis=1):
	num+=1

	# Find the right spot on the plot
	plt.subplot(3,3, num)

	# Plot the lineplot
	plt.plot(df['x'], df[column], marker='', color=palette(num), linewidth=1.9, alpha=0.9, label=column)

	# Same limits for everybody!
	plt.xlim(0,10)
	plt.ylim(-2,22)

	# Not ticks everywhere
	if num in range(7) :
		plt.tick_params(labelbottom='off')
	if num not in [1,4,7] :
		plt.tick_params(labelleft='off')

	# Add title
	plt.title(column, loc='left', fontsize=12, fontweight=0, color=palette(num) )

# general title
plt.suptitle("How the 9 students improved\nthese past few days?", fontsize=13, fontweight=0, color='black', style='italic', y=1.02)

# Axis title
plt.text(0.5, 0.02, 'Time', ha='center', va='center')
plt.text(0.06, 0.5, 'Note', ha='center', va='center', rotation='vertical')

Right graph

# libraries and data
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd

# Make a data frame
df=pd.DataFrame({'x': range(1,11), 'y1': np.random.randn(10), 'y2': np.random.randn(10)+range(1,11), 'y3': np.random.randn(10)+range(11,21), 'y4': np.random.randn(10)+range(6,16), 'y5': np.random.randn(10)+range(4,14)+(0,0,0,0,0,0,0,-3,-8,-6), 'y6': np.random.randn(10)+range(2,12), 'y7': np.random.randn(10)+range(5,15), 'y8': np.random.randn(10)+range(4,14), 'y9': np.random.randn(10)+range(4,14) })

# Initialize the figure
plt.style.use('seaborn-darkgrid')

# create a color palette
palette = plt.get_cmap('Set1')

# multiple line plot
num=0
for column in df.drop('x', axis=1):
	num+=1

	# Find the right spot on the plot
	plt.subplot(3,3, num)

	# plot every groups, but discreet
	for v in df.drop('x', axis=1):
		plt.plot(df['x'], df[v], marker='', color='grey', linewidth=0.6, alpha=0.3)

	# Plot the lineplot
	plt.plot(df['x'], df[column], marker='', color=palette(num), linewidth=2.4, alpha=0.9, label=column)

	# Same limits for everybody!
	plt.xlim(0,10)
	plt.ylim(-2,22)

	# Not ticks everywhere
	if num in range(7) :
		plt.tick_params(labelbottom='off')
	if num not in [1,4,7] :
		plt.tick_params(labelleft='off')

	# Add title
	plt.title(column, loc='left', fontsize=12, fontweight=0, color=palette(num) )

# general title
plt.suptitle("How the 9 students improved\nthese past few days?", fontsize=13, fontweight=0, color='black', style='italic', y=1.02)

# Axis title
plt.text(0.5, 0.02, 'Time', ha='center', va='center')
plt.text(0.06, 0.5, 'Note', ha='center', va='center', rotation='vertical')