Pandas: map dataframe column to list and assign binary value?

Question

I have a dataframe that looks like this:

df = pd.read.csv("variants.csv")
print(df)
    Sample Position Reference Alt
    Sample1 123 C T
    Sample2 123 C T
    Sample3 1234 C G

and a list of 'Positions' of interest:

pos = [123, 1334, 1443, 133]

I want to map the column of 'Position' to my list and create a new column in the dataframe where if 'Position' exists == 1 else I assign a value of 0. Example:

        Sample Position Reference Alt Value
        Sample1 123 C T 1
        Sample2 123 C T 1
        Sample3 1234 C G 0

How can I do this in Pandas or another way? Apologies as I'm a beginner to python.

jezrael · Accepted Answer · 2020-09-08 12:53:34Z

3

Use Series.isin for mask and then convert to 1,0 from True, False by Series.view:

df['Value'] = df.Position.isin(pos).view('i1')

Or by cast to integers by Series.astype:

df['Value'] = df.Position.isin(pos).astype('int')

Or with numpy.where:

df['Value'] = np.where(df.Position.isin(pos), 1, 0)

answered Sep 8, 2020 at 12:53

jezrael

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1 Comment

Hryhorii Pavlenko Over a year ago

never seen view before, nice!

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