I want to perform the pct_change() operation in pandas without using the operation.
For example, I have an array a = [1, 2, 3, 4].
a.pct_change() would result in [NaN, 1.0, 0.5, 0.333].
I want to get the same result without using pct_change().
I attempted doing (a[1:]/a) - 1 but don't get the expected result.