Change grid interval and specify tick labels in Matplotlib

Question

I am trying to plot counts in gridded plots, but I haven't been able to figure out how to go about it.

I want:

1. to have dotted grids at an interval of 5;

2. to have major tick labels only every 20;

3. for the ticks to be outside the plot; and

4. to have "counts" inside those grids.

I have checked for potential duplicates, such as here and here, but have not been able to figure it out.

This is my code:

import matplotlib.pyplot as plt from matplotlib.ticker import MultipleLocator, FormatStrFormatter  for key, value in sorted(data.items()):     x = value[0][2]     y = value[0][3]     count = value[0][4]      fig = plt.figure()     ax = fig.add_subplot(111)      ax.annotate(count, xy = (x, y), size = 5)     # overwrites and I only get the last data point      plt.close()     # Without this, I get a "fail to allocate bitmap" error.  plt.suptitle('Number of counts', fontsize = 12) ax.set_xlabel('x') ax.set_ylabel('y') plt.axes().set_aspect('equal')  plt.axis([0, 1000, 0, 1000]) # This gives an interval of 200.  majorLocator   = MultipleLocator(20) majorFormatter = FormatStrFormatter('%d') minorLocator   = MultipleLocator(5) # I want the minor grid to be 5 and the major grid to be 20. plt.grid()  filename = 'C:\Users\Owl\Desktop\Plot.png' plt.savefig(filename, dpi = 150) plt.close() 

This is what I get.

I also have a problem with the data points being overwritten.

Could anybody PLEASE help me with this problem?

Answer 1

There are several problems in your code.

First the big ones:

1. You are creating a new figure and a new axes in every iteration of your loop → put fig = plt.figure and ax = fig.add_subplot(1,1,1) outside of the loop.

2. Don't use the Locators. Call the functions ax.set_xticks() and ax.grid() with the correct keywords.

3. With plt.axes() you are creating a new axes again. Use ax.set_aspect('equal').

The minor things: You should not mix the MATLAB-like syntax like plt.axis() with the objective syntax. Use ax.set_xlim(a,b) and ax.set_ylim(a,b)

This should be a working minimal example:

import numpy as np import matplotlib.pyplot as plt  fig = plt.figure() ax = fig.add_subplot(1, 1, 1)  # Major ticks every 20, minor ticks every 5 major_ticks = np.arange(0, 101, 20) minor_ticks = np.arange(0, 101, 5)  ax.set_xticks(major_ticks) ax.set_xticks(minor_ticks, minor=True) ax.set_yticks(major_ticks) ax.set_yticks(minor_ticks, minor=True)  # And a corresponding grid ax.grid(which='both')  # Or if you want different settings for the grids: ax.grid(which='minor', alpha=0.2) ax.grid(which='major', alpha=0.5)  plt.show() 

Output is this: