How to invert scatter plot axis

[Mark17]

Hi all,

Here's some code:

import pandas as pd
import matplotlib.pyplot as plt
import time
import numpy as np

start_time = time.time()

df = pd.DataFrame(columns=['DTE', 'Long Delta', 'Short Delta', 'Delta Spread'])

# Checking all permutations covered by program:  
for dte in range(30,61):
    long_delta = np.arange(-0.1,-0.35,-0.05)
    short_delta = np.arange(-0.25,-0.50,-0.05)
    if dte == 30:
        for ld in long_delta:
            for sd in short_delta:  
                plt.scatter(ld,sd)
                
plt.tight_layout() #to prevent axis labels from being cut off in saved figure
plt.xlabel('Long Delta')
plt.ylabel('Short Delta')
end_time = time.time()
print('Elapsed time is {:.0f}ms'.format(1000*(end_time-start_time)))

How do I reverse the axes on the graph so they go from largest to smallest (left to right and down to up)?

Mark

[jefsummers]

import matplotlib.pyplot as plt

ex = [0,0.2,0.5,1]
ey = [0.1, 1,2.5,4]

#plot normal
plaid = plt.scatter(ex, ey)

#now reverse axes
fig, ax = plt.subplots()
ax.scatter(ex, ey)
ax.set_xlim(1,0)
ax.set_ylim(5,-1)
ax.grid = True
plt

You might use plt.show() - I was in a notebook so just used plt

[Mark17]

import matplotlib.pyplot as plt

ex = [0,0.2,0.5,1]
ey = [0.1, 1,2.5,4]

#plot normal
plaid = plt.scatter(ex, ey)

#now reverse axes
fig, ax = plt.subplots()
ax.scatter(ex, ey)
ax.set_xlim(1,0)
ax.set_ylim(5,-1)
ax.grid = True
plt

You might use plt.show() - I was in a notebook so just used plt

So I have to use the object-oriented approach with fig and ax to invert axes?

Also, when I initially did this I didn't know what the min and max were going to be: matpltlib calculated that on its own. Do I have to run once to see what the min and max are and then take those values to build into the code?

Thanks jefsummers!
Mark

[jefsummers]

I believe that is the way to get access to the axes.
Change lines 11 and 12 to

ax.set_xlim(max(ex), min(ex))
ax.set_ylim(max(ey),min(ey))