Pandas dataframe: propagate True values if timestamp is identical

Question

Best described by an example. Input is

   ts    val
0   10  False
1   20   True
2   20  False
3   30   True
4   40  False
5   40  False
6   40  False
7   60   True
8   60  False

desired output is

   ts    val
0   10  False
1   20   True
2   20   True
3   30   True
4   40  False
5   40  False
6   40  False
7   60   True
8   60  True

The idea is as follows: if we see at least one True value inside the same ts cluster(ie same ts value), make all other values True that have the exact same timestamp.

Answer 1

You can use groupby on column 'ts', and then apply using .any() to determine whether any of val is True in the cluster/group.

import pandas as pd

# your data
# =====================
print(df)

Out[58]: 
   ts    val    data
0  10  False  0.3332
1  20   True -0.6877
2  20  False -0.6004
3  30   True  0.1922
4  40  False  0.2472
5  40  False -0.0117
6  40  False  0.8607
7  60   True -1.1464
8  60  False  0.0698


# processing
# =====================
# as suggested by @DSM, transform is best way to do it
df['val'] = df.groupby('ts')['val'].transform(any)

Out[61]: 
   ts    val    data
0  10  False  0.3332
1  20   True -0.6877
2  20   True -0.6004
3  30   True  0.1922
4  40  False  0.2472
5  40  False -0.0117
6  40  False  0.8607
7  60   True -1.1464
8  60   True  0.0698