I have a data frame like that :

I want to compare id column for each pairs. So between the row 0 and 1, between the row 2 and 3 etc. In others words I want to compare even rows with odd rows and keep same id pairs rows.

My ideal output would be :

I tried that but it did not work :

df = df[
    df[::2]["id"] ==df[1::2]["id"]
]

CodePudding user response：

You can use a GroupBy.transform approach:

# for each pair, is there only one kind of Id?
out = df[df.groupby(np.arange(len(df))//2)['Id'].transform('nunique').eq(1)]

Or, more efficient, using the underlying numpy array:

# convert to numpy
a = df['Id'].to_numpy()

# are the odds equal to evens?
out = df[np.repeat((a[::2]==a[1::2]), 2)]

output:

   Index      Time  Id
2      2  10:10:02  12
3      3  10:10:04  12
4      4  10:10:06  13
5      5  10:10:07  13
6      6  10:10:08  11
7      7  10:10:10  11