Changed pct_change parameters to calculate pct_change right-to-left f…

[andrei-assa]

…or axis=1.

• closes Pandas dataframe pct_change function arguments #39672
• Ensure all linting tests pass, see here for how to run them
• For axis = 1, periods = -periods.

[pep8speaks]

Hello @andrei-assa! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file pandas/core/generic.py:

Line 10209:89: E501 line too long (91 > 88 characters)
Line 10211:89: E501 line too long (90 > 88 characters)

[jreback]

tests pls

[MarcoGorelli]

closes #39672

The issue just involves slightly changing the example in the docs, the source code shouldn't need changing

[bashtage]

The issue just involves slightly changing the example in the docs, the source code shouldn't need changing

Fully agree. It is not reasonable to change the behavior of pct_change when applied across columns. It should be the case that pct_change(periods=n) should be the change from df.iloc[:-n] to df.iloc[n:] for positive n and df.iloc[n:] to df.iloc[:-n] for negative n. Adding an axis shouldn't change this behavior, and when computed across columns pct_change(periods=n) should be the change from df.iloc[:,:-n] to df.iloc[:,n:] for positive n and df.iloc[:,n:] to df.iloc[:,:-n] for negative n

[MarcoGorelli]

closed in #40266 , thanks anyway @andrei-assa for your PR