Get Data Points From A Histogram In Python

I made a histogram of the 'cdf' (cumulative distribution) of a function. The histogram is basically No. of counts vs. luminosity. Now, how do I extract data points from a histogram

Solution 1:

You've already got a list of ls, so I'm not sure what you mean by that last statement, so maybe I've misinterpreted the question.

To get the values from a histogram, plt.hist returns them, so all you have to do is save them.

If you don't save them, the interpreter just prints the output:

In [34]: x = np.random.rand(100)

In [35]: plt.hist(x)
Out[35]: 
(array([ 11.,   9.,  10.,   6.,   8.,   8.,  10.,  10.,  11.,  17.]),
 array([ 0.00158591,  0.100731  ,  0.19987608,  0.29902116,  0.39816624,
        0.49731133,  0.59645641,  0.69560149,  0.79474657,  0.89389165,
        0.99303674]),
 <a list of 10 Patch objects>)

So, to save them, do:

counts, bins, bars = plt.hist(x)

Solution 2:

You can also retrieve info from an already plotted histogram. For example:

x = np.random.rand(100)
plt.hist(x)

ax = plt.gca() # get axis handle

You can access to each individual bar using patches. Then .get_xy() will give you the x-y coordiate of a single bar (lower left corner), .get_width() will give width of the bar, and .get_height() will give the height of the bar (which is probably what you want).

p = ax.patches  # There are 10 patches
p[0].get_xy()
>> (0.011714084185001972, 0.0)
p[0].get_width()
>>0.09871329223828645
p[0].get_height()
>>8.0

So to retrieve all the heights:

heights = [patch.get_height() for patch in p]

And to reproduce the histogram:

plt.bar(range(len(heights)), heights)

Solution 3:

if you want to get the assignments to bins, You can do it in the following way as explained here Which elements of list go into which histogram bins?

nbins=7
# Some example data
A = np.random.randint(0, 10, 10) 
B = np.random.rand(10)

counts, binEdges=np.histogram(A,bins=nbins)
>>> binEdges, np.digitize(A, binEdges)
array([ 0.        ,  1.28571429,  2.57142857,  3.85714286,  5.14285714,
    6.42857143,  7.71428571,  9.        ])