How to Set Y-Axis Range to Enrich Visualization in Multiple Subplot Layouts?

Setting Subplot Axis Range

Background

When working with multiple subplots in a visualization, it becomes necessary to control the axis range of each individual subplot to ensure proper data representation. This question explores how to set the y-axis range of a second subplot within a two-subplot layout. The issue arises when an FFT plot exhibits an outlier spike, rendering the desired data invisible.

Solution

To address this issue, use pylab.ylim([bottom, top]) after the plot has been created. The bottom and top arguments define the lower and upper bounds of the axis range, respectively.

<code class="python">import numpy, scipy, pylab, random

xs = []
rawsignal = []
with open("test.dat", 'r') as f:
    for line in f:
        if line[0] != '#' and len(line) > 0:
            xs.append(int(line.split()[0]))
            rawsignal.append(int(line.split()[1]))

h, w = 3, 1
pylab.figure(figsize=(12,9))
pylab.subplots_adjust(hspace=.7)

pylab.subplot(h,w,1)
pylab.title("Signal")
pylab.plot(xs,rawsignal)

pylab.subplot(h,w,2)
pylab.title("FFT")
fft = scipy.fft(rawsignal)
pylab.plot(abs(fft))
pylab.ylim([0,1000]) # Set the y-axis range

pylab.savefig("SIG.png",dpi=200)
pylab.show()</code>

Improvement

1. Migrate from Pylab to Matplotlib's pyplot

As of 2021, Matplotlib strongly discourages the use of pylab. Instead, it is recommended to importpyplot specifically:

<code class="python">from matplotlib import pyplot as plt</code>

2. Use plt.ylim() Instead of pylab.ylim()

The correct syntax for setting the y-axis range using pyplot is plt.ylim(). Its usage is similar to pylab.ylim().

<code class="python">plt.ylim(0, 100) </code>

3. Set Minimum X-Axis Value

In addition to adjusting the y-axis range, consider setting the minimum x-axis value to ensure the entire range of the FFT plot is visible.

<code class="python">plt.xlim(1, 1000)</code>

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