[FIXED] Pandas percentage change matrix

Issue

I have a data frame:

	product	cost
0	product a	56
1	product b	59
2	product c	104

I'd like to make a percentage change matrix like:

	product a	product b	product c
product a		-5.08%	-46.15%
product b	5.36%		-43.30%
product c	85.71%	76.27%

There could be n number of products.

1. How do I this using pandas?

2. How do I get the highest / lowest percentage change products? i.e. Highest: product a vs. product c. Lowest: product c vs. product a.

Thank you for your help.

Solution

Use numpy broadcasting:

# convert columns to arrays
idx = df['product'].to_numpy()
cost = df['cost'].to_numpy()

# compute the percentage change using broadcasting
# convert to DataFrame
out = pd.DataFrame(((cost[:,None]-cost)/cost*100).round(2),
                   index=idx, columns=idx)

# optional, set NaNs in the diagonal
np.fill_diagonal(out.values, np.nan)

print(out)

Output:

           product a  product b  product c
product a        NaN      -5.08     -46.15
product b       5.36        NaN     -43.27
product c      85.71      76.27        NaN

Answered By - mozway