pandasdataframedata-sciencedata-munging

pandas series mark all the rows between two values

I have a series ( a single col in a df) with 3 possible values:

Stable, Increase, Decresae

, and I want to mark all the areas between a Increase to the subsequent Decrease. So for the values:

Stable
Stable
Stable
Increase
Increase
Stable
Stable
Decrease
Stable
Increase
Stable
Decrease

I will get: -,-,-,+,+,+,+,-,-,+,+,- What is the best way to do so?

Solution

  • map True on Increase and False on Decrease, then ffill. Finally map the +/- with numpy.where:

    s = df['col'].map({'Increase': True, 'Decrease': False}).ffill().fillna(False)
df['indicator'] = np.where(s, '+', '-')

    As a one-liner:

    df['indicator'] = np.where(df['col'].map({'Increase': True, 'Decrease': False})
                                    .ffill().fillna(False),
                           '+', '-')

    Output:

             col indicator
0     Stable         -
1     Stable         -
2     Stable         -
3   Increase         +
4   Increase         +
5     Stable         +
6     Stable         +
7   Decrease         -
8     Stable         -
9   Increase         +
10    Stable         +
11  Decrease         -

    Intermediates:

             col    map  ffill+fillna indicator
0     Stable    NaN         False         -
1     Stable    NaN         False         -
2     Stable    NaN         False         -
3   Increase   True          True         +
4   Increase   True          True         +
5     Stable    NaN          True         +
6     Stable    NaN          True         +
7   Decrease  False         False         -
8     Stable    NaN         False         -
9   Increase   True          True         +
10    Stable    NaN          True         +
11  Decrease  False         False         -