Find the increase, decrease in a column of pandas Dataframe

Question

I have a dataframe and I want to check whether the elements in the column \"GDP\" increase or decrease in comparison to their previous value to create column

Answer 1

out = np.where(df.GDP.diff() > 0, 'increase', 'decline')
out[0] = '------'

Answer 2

numpy concept #1

set up category array and slice it

cats = np.array(['decline', '------', 'increase'])
df.assign(
    change=cats[np.sign(
        np.append(0, np.diff(df.GDP.values, 1))
    ).astype(np.uint8) + 1])

numpy concept #2

nested np.where

diffs = df.GDP.diff()
df.assign(
    change=np.where(
        diffs > 0, 'increase', np.where(
            diffs < 0, 'decline', '------')))

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Result