Consider the following toy code that performs a simplified version of my actual question:
import pandas
df = pandas.DataFrame(
{
'n_event': [1,2,3,4,5],
'some column': [0,1,2,3,4],
}
)
df = df.set_index(['n_event'])
print(df)
resampled_df = df.sample(frac=1, replace=True)
print(resampled_df)
The resampled_df
is, as it name suggests, a resampled version of the original one (with replacement). This is exactly what I want. An example output of the previous code is
some column
n_event
1 0
2 1
3 2
4 3
5 4
some column
n_event
4 3
1 0
4 3
4 3
2 1
Now for my actual question I have the following dataframe:
import pandas
df = pandas.DataFrame(
{
'n_event': [1,1,2,2,3,3,4,4,5,5],
'n_channel': [1,2,1,2,1,2,1,2,1,2],
'some column': [0,1,2,3,4,5,6,7,8,9],
}
)
df = df.set_index(['n_event','n_channel'])
print(df)
which looks like
some column
n_event n_channel
1 1 0
2 1
2 1 2
2 3
3 1 4
2 5
4 1 6
2 7
5 1 8
2 9
I want to do exactly the same as before, resample with replacements, but treating each group of rows with the same n_event
as a single entity. A hand-built example of what I want to do can look like this:
some column
n_event n_channel
2 1 2
2 3
2 1 2
2 3
3 1 4
2 5
1 1 0
2 1
5 1 8
2 9
As seen, each n_event
was treated as a whole and things within each event were no mixed up.
How can I do this without proceeding by brute force (ie without for
loops, etc)?
I have tried with df.sample(frac=1, replace=True, ignore_index=False)
and a few things using group_by
without success.
Would a pivot()
/ melt()
sequence work for you?
Use pivot()
to from long to wide (make each group a single row).
Do the sampling.
Then back from wide to long using melt()
.
Don't have time to work out a full answer but thought I would get this idea to you in case it might help you.
Following the suggestion of jch I was able to find a solution by combining pivot
and stack
:
import pandas
df = pandas.DataFrame(
{
'n_event': [1,1,2,2,3,3,4,4,5,5],
'n_channel': [1,2,1,2,1,2,1,2,1,2],
'some column': [0,1,2,3,4,5,6,7,8,9],
'other col': [5,6,4,3,2,5,2,6,8,7],
}
)
resampled_df = df.pivot(
index = 'n_event',
columns = 'n_channel',
values = set(df.columns) - {'n_event','n_channel'},
)
resampled_df = resampled_df.sample(frac=1, replace=True)
resampled_df = resampled_df.stack()
print(resampled_df)
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