When I plot 2 columns one over the other, a different graph is plotted

问题

I have 2 columns from 2 np.arrays of the same size. When I plot the only the one I get this result:

plt.figure(figsize=(70,10))

for i,h in enumerate(clean_head):

    plt.subplot(1,6,i+1)
    #plt.hist(non_fire[:,i],alpha=.3)
    plt.hist(fire[:,i],alpha=.3)
    plt.title(clean_head[i])

   # plt.tight_layout()

When I plot both I get this:

plt.figure(figsize=(70,10))

for i,h in enumerate(clean_head):

    plt.subplot(1,6,i+1)
    plt.hist(non_fire[:,i],alpha=.3)
    plt.hist(fire[:,i],alpha=.3)
    plt.title(clean_head[i])

   # plt.tight_layout()

Where no one of the two histograms is the same with the initial. I dont understand which is the pink and which is the lightblue graph.

I have 16 more plots like that and I have the same problem with all of them.

回答1:

in the second set of plots the blue histogram is for the "non-fire"-case and the orange one is for the "fire"-case. If you would plot a third histogram, it would be green. In general you can change the color of a given histogram using the parameter color.

The reason why your histograms change is that your arrays have different value ranges. You can fix this by explicitly giving bins the the function:

import matplotlib.pyplot as plt
import numpy as np

a = np.random.rand(100)
b = np.random.rand(100)*2

bins = np.linspace(min(np.min(a), np.min(b)), max(np.max(a), np.max(b)), 10)

plt.figure(figsize=(7,5))
plt.hist(a,alpha=.3, bins=bins)
#plt.hist(b,alpha=.3, bins=bins) #toggle this to see the effect

Also note that histogram function returns the list of bins that it uses.

Hope that helps.

来源：https://stackoverflow.com/questions/55377172/when-i-plot-2-columns-one-over-the-other-a-different-graph-is-plotted

标签

python

plot

histogram