Python Matplotlib subplot How to set the axis range

Question

How can I set the y axis range of the second subplot to e g   0 1000    The FFT plot of my data  a column in a text file  results in a  inf    spike so that the actual data is not visible   pylab ylim  0 1000     has no effect  unfortunately  This is the whole script     based on http   www swharden com blog 2009-01-21-signal-filtering-with-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   gt  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 axis  None None 0 1000   pylab ylim  0 1000   pylab plot abs fft    pylab savefig  SIG png  dpi 200  pylab show     Other improvements are also appreciated

User · Answer

Using axes objects is a great approach for this  It helps if you want to interact with multiple figures and sub-plots  To add and manipulate the axes objects directly   import matplotlib pyplot as plt fig   plt figure figsize  12 9    signal axes   fig add subplot 211  signal axes plot xs rawsignal   fft axes   fig add subplot 212  fft axes set title  FFT   fft axes set autoscaley on False  fft axes set ylim  0 1000   fft   scipy fft rawsignal  fft axes plot abs fft    plt show

User · Answer

Sometimes you really want to set the axes limits before you plot the data   In that case  you can set the  autoscaling  feature of the Axes or AxesSubplot object   The functions of interest are set autoscale on  set autoscalex on  and set autoscaley on   In your case  you want to freeze the y axis  limits  but allow the x axis to expand to accommodate your data   Therefore  you want to change the autoscaley on property to False   Here is a modified version of the FFT subplot snippet from your code   fft axes   pylab subplot h w 2  pylab title  FFT   fft   scipy fft rawsignal  pylab ylim  0 1000   fft axes set autoscaley on False  pylab plot abs fft

User · Answer

You have pylab ylim  pylab ylim  0 1000    Note  The command has to be executed after the plot  Update 2021 Since the use of pylab is now strongly discouraged by matplotlib  you should instead use pyplot  from matplotlib import pyplot as plt plt ylim 0  100    corresponding function for the x-axis plt xlim 1  1000

User · Answer

If you know the exact axis you want  then  pylab ylim  0 1000    works as answered previously  But if you want a more flexible axis to fit your exact data  as I did when I found this question  then set axis limit to be the length of your dataset  If your dataset is fft as in the question  then add this after your plot command   length    len fft   pylab ylim  0 length

User · Answer

If you have multiple subplots  i e   fig  ax   plt subplots 4  2    You can use the same y limits for all of them  It gets limits of y ax from first plot   plt setp ax  ylim ax 0 0  get ylim

[python] Python, Matplotlib, subplot: How to set the axis range?

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