In a matplotlib plot consisting of histogram subplots, how can the height and bar edges of one histogram be changed? - matplotlib

Question

I've got a little function that generates a plot of two subplots. One subplot is two histograms overlaid and the other subplot is the results of dividing one histogram by the other.
For the second subplot, I don't know how to remove the edges between histogram bars (like the one above it) and I don't know how to reduce its height (such that it is, say, half the height of the one above it). I'm also not sure how to set the title to the very top of the plot.
How could these things be done?
My code is as follows:
import numpy
import matplotlib.pyplot
import datavision # sudo pip install datavision
import shijian # sudo pip install shijian
def main():
a = numpy.random.normal(2, 2, size = 120)
b = numpy.random.normal(2, 2, size = 120)
save_histogram_comparison_matplotlib(
values_1 = a,
values_2 = b,
label_1 = "a",
label_2 = "b",
normalize = True,
label_ratio_x = "frequency",
label_y = "",
title = "comparison of a and b",
filename = "test.png"
)
def save_histogram_comparison_matplotlib(
values_1 = None,
values_2 = None,
filename = None,
number_of_bins = None,
normalize = True,
label_x = "",
label_y = None,
label_ratio_x = "frequency",
label_ratio_y = "ratio",
title = None,
label_1 = "1",
label_2 = "2",
overwrite = True,
LaTeX = False
):
matplotlib.pyplot.ioff()
if LaTeX is True:
matplotlib.pyplot.rc("text", usetex = True)
matplotlib.pyplot.rc("font", family = "serif")
if number_of_bins is None:
number_of_bins_1 = datavision.propose_number_of_bins(values_1)
number_of_bins_2 = datavision.propose_number_of_bins(values_2)
number_of_bins = int((number_of_bins_1 + number_of_bins_2) / 2)
if filename is None:
filename = shijian.propose_filename(
filename = title.replace(" ", "_") + ".png",
overwrite = overwrite
)
values = []
values.append(values_1)
values.append(values_2)
bar_width = 0.8
figure, (axis_1, axis_2) = matplotlib.pyplot.subplots(nrows = 2)
ns, bins, patches = axis_1.hist(
values,
normed = normalize,
histtype = "stepfilled",
bins = number_of_bins,
alpha = 0.5,
label = [label_1, label_2],
rwidth = bar_width,
linewidth = 0
)
axis_1.legend()
axis_2.bar(
bins[:-1],
ns[0] / ns[1],
edgecolor = "#ffffff", # "none"
alpha = 1,
width = bins[1] - bins[0]
)
axis_1.set_xlabel(label_x)
axis_1.set_ylabel(label_y)
axis_2.set_xlabel(label_ratio_x)
axis_2.set_ylabel(label_ratio_y)
matplotlib.pyplot.title(title)
matplotlib.pyplot.savefig(filename)
matplotlib.pyplot.close()
if __name__ == "__main__":
main()

Answer 1

You have 3 questions:
1. How to remove the edges between histogram bars
Here, you can set the linewidth to 0 for the call to bar:
axis_2.bar(
bins[:-1],
ns[0] / ns[1],
linewidth=0,
alpha = 1,
width = bins[1] - bins[0]
)
2. How to reduce the height of the second subplot
Here, we can send kwargs to gridspec when we create the subplots. The relevant option is height_ratios. We send them using the gridspec_kw option to subplots. If we set it to (2,1), that makes the first subplot twice the height of the second one.
figure, (axis_1, axis_2) = matplotlib.pyplot.subplots(
nrows = 2,
gridspec_kw={'height_ratios':(2,1)}
)
3. How to set the title to the very top of the plot
When you call matplotlib.pyplot.title(title), that is actually setting the title of the currently active subplot axes, which in this case is axis_2. To set the title of the overall figure, you can set the suptitle:
matplotlib.pyplot.suptitle(title)
Or alternatively, since you already named your figure, you can use:
figure.suptitle(title)
And likewise, you could use:
figure.savefig(filename)
to save a few keystrokes.
Putting it all together: