blz blz - 6 months ago 12
Python Question

Why is pandas inserting spaces in my histogram?

Example data can be found here in CSV format.

Given the following code:

figure()
grp.vis.plot(kind='hist', alpha=.5, normed=True)
show()


I obtain the following figure:

enter image description here

Why is pandas inserting gaps in the figure? The values range from 0 to 7, and are all represented, so I see no reason why this should happen.

Thanks very much in advance!

Answer

Because parameter bins with default value 10 is in hist:

grp.vis.plot(kind='hist', alpha=.5, bins=7, normed=True)

graph

If omit rwidth:

grp.vis.plot(kind='hist', alpha=.5, bins=7)

graph1

Docs:

bins : integer or array_like, optional

If an integer is given, bins + 1 bin edges are returned, consistently with numpy.histogram() for numpy version >= 1.3.

Unequally spaced bins are supported if bins is a sequence.

default is 10

rwidth : scalar or None, optional

The relative width of the bars as a fraction of the bin width. If None, automatically compute the width.

Ignored if histtype is ‘step’ or ‘stepfilled’.

Default is None

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