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Pandas COUNTIF based on column value

I am trying to essentially do COUNTIF in pandas to count how many items in a row match the number in the first column.

Dataframe:

a b c d
1 2 3 1
2 3 4 2
3 5 6 3

So, I want to count the instances in line (b, c, d) that match a. Line 1, for example, should be 1, since only d matches a.

I searched a bit for this, but so far only found examples where its total (e.g. counting all values ​​greater than 0) but not based on the dataframe column. I am guessing its some form of logic that masks based on the column but df == df.a

doesn't seem to work

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2 answers


You can use eq

which you can pass to a parameter axis

to indicate the direction of the comparison, then you can do the sum of the string to count the number of values ​​matched:



df.eq(df.a, axis=0).sum(1) - 1

#0    1
#1    1
#2    1
#dtype: int64
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df.apply(lambda x: (x == x[0]).sum()-1,axis=1)


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