# Plot histogram with colors taken from colormap

## Question:

I want to plot a simple 1D histogram where the bars should follow the color-coding of a given colormap.

Here’s an `MWE`

:

```
import numpy as n
import matplotlib.pyplot as plt
# Random gaussian data.
Ntotal = 1000
data = 0.05 * n.random.randn(Ntotal) + 0.5
# This is the colormap I'd like to use.
cm = plt.cm.get_cmap('RdYlBu_r')
# Plot histogram.
n, bins, patches = plt.hist(data, 25, normed=1, color='green')
plt.show()
```

which outputs this:

Instead of the color being `green`

for the entire histogram, I’d like the columns to follow a color-coding given by the colormap defined in `cm`

and the values of the `bins`

. This would mean that bins closer to zero (*not* in height but in position) should look bluer and those closer to one redder, according to the chosen colormap `RdYlBu_r`

.

Since `plt.histo`

doesn’t take a `cmap`

argument I don’t know how to tell it to use the colormap defined in `cm`

.

## Answers:

The `hist`

command returns a list of patches, so you can iterate over them and set their color like so:

```
import numpy as n
import matplotlib.pyplot as plt
# Random gaussian data.
Ntotal = 1000
data = 0.05 * n.random.randn(Ntotal) + 0.5
# This is the colormap I'd like to use.
cm = plt.cm.get_cmap('RdYlBu_r')
# Plot histogram.
n, bins, patches = plt.hist(data, 25, normed=1, color='green')
bin_centers = 0.5 * (bins[:-1] + bins[1:])
# scale values to interval [0,1]
col = bin_centers - min(bin_centers)
col /= max(col)
for c, p in zip(col, patches):
plt.setp(p, 'facecolor', cm(c))
plt.show()
```

To get the colors, you need to call the colormap with a value between 0 and 1. Resulting figure:

An alternative approach is to use `plt.bar`

which takes in a list of colors. To determine the widths and heights you can use `numpy.histogram`

. Your colormap can be used by finding the range of the x-values and scaling them from 0 to 1.

```
import numpy as n
import matplotlib.pyplot as plt
# Random gaussian data.
Ntotal = 1000
data = 0.05 * n.random.randn(Ntotal) + 0.5
# This is the colormap I'd like to use.
cm = plt.cm.get_cmap('RdYlBu_r')
# Get the histogramp
Y,X = n.histogram(data, 25, normed=1)
x_span = X.max()-X.min()
C = [cm(((x-X.min())/x_span)) for x in X]
plt.bar(X[:-1],Y,color=C,width=X[1]-X[0])
plt.show()
```

While it isn’t what you asked for, if someone else stumbles across this (like I did) looking for the way to do the coloration by height of the bins instead of order, the following code based on Bas’s answer would work:

```
import numpy as np
import matplotlib.pyplot as plt
Ntotal = 1000
data = 0.05 * np.random.randn(Ntotal) + 0.5
cm = plt.cm.get_cmap('RdYlBu_r')
n, bins, patches = plt.hist(data, 25, normed=1, color='green')
# To normalize your values
col = (n-n.min())/(n.max()-n.min())
for c, p in zip(col, patches):
plt.setp(p, 'facecolor', cm(c))
plt.show()
```

I like Bas Swinckels answer, but given that the colormap cm take as parameter a value between 0 and 1, a simpler algorithm would be like this

```
import matplotlib.pyplot as plt
Ntotal = 1000
data = 0.05 * n.random.randn(Ntotal) + 0.5
cm = plt.cm.RdBu_r
n, bins, patches = plt.hist(data, 25, normed=1, color='green')
for i, p in enumerate(patches):
plt.setp(p, 'facecolor', cm(i/25)) # notice the i/25
plt.show()
```