Plotting histogram in python

Question

I wrote the following program in python to obtain equi-width histograms. But when I am plotting it I am getting a single line in figure instead of a histogram. Can someone please help me figure out as to where am I going wrong.

import numpy as np
import matplotlib.pyplot as plt

for num in range(0,5):
    hist, bin_edges = np.histogram([1000, 98,99992,8474,95757,958574,97363,97463,1,4,5], bins = 5)
    plt.bar(bin_edges[:-1], hist, width = 1000)
    plt.xlim(min(bin_edges), max(bin_edges))
    plt.show()

Additionally I want to label each plot obtained with its "num" value..which range from 0 to 5. In the example given above although I have kept my data constant, but I intend to change my data for different "num" values.

BrenBarn · Accepted Answer · 2015-02-07 03:20:05Z

Look at your bin edges:

>>> bin_edges
array([  1.00000000e+00,   1.91715600e+05,   3.83430200e+05,
         5.75144800e+05,   7.66859400e+05,   9.58574000e+05])

Your bin positions range from 1 to approximately 1 million, but you only gave the bars a width of 1000. Your bars, where they exist at all, are too skinny to be seen. Also, most of the bars have sero height, because most of the bins are empty:

>>> hist
array([10,  0,  0,  0,  1])

The "line" you see is the last bin, with one element. This bin covers a span of approximately 200000, but the bar width is only 1000, so it is very thin relative to the amount of space it is supposed to cover. The bar of height 10 is also there, but it's also very skinny, and jammed up against the left edge of the plot, so it's basically invisible.

It doesn't make sense to try to use constant-width bars while also placing them at x-coordinates that correspond to their size. By putting the bars at those x-coordinates, you are already spacing them out proportional to the bin widths; making the bars skinnier doesn't bring them closer together, it just makes them invisible.

If you want to use constant-width bars, you should put them at sequential X positions and use labels on the axis to show the values the bins represent. Here's a simple example with your data:

plt.bar(np.arange(len(bin_edges)-1), hist, width=1)
plt.xticks((np.arange(len(bin_edges))-0.5)[1:], bin_edges[:-1])

enter image description here

You'll have to decide how you want to format those labels.

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