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pythonpandas
Winston
Winston

Reputation: 326

Pandas sort column but keep elements of the same category together

I have a dataframe with two columns. One is numeric and the other is categorical. For example,

   c1   c2
0  15   A
1  11   A
2  12   B
3  40   C

I want to sort by c1 but keep rows with the same c2 value together (so all the A's stay together). In categories where there are multiple entries, we sort by the largest value in that category.

So end result would be

   c1   c2
0  40   C
1  15   A
2  11   A
3  12   B

How should I do this? Thanks

Upvotes: 1

Views: 1943

Answers (3)

Henry Ecker
Henry Ecker

Reputation: 35676

We can create a temp column withgroupby transform max to get the max value per group sort_values with ascending False then drop the added column.

df = (
    df.assign(key=df.groupby('c2')['c1'].transform('max'))
        .sort_values(['key', 'c2', 'c1'], ascending=False, ignore_index=True)
        .drop(columns=['key'])
)

df:

   c1 c2
0  40  C
1  15  A
2  11  A
3  12  B

Upvotes: 6

Acccumulation
Acccumulation

Reputation: 3591

df.sort_values(by = ['c2', 'c1'], ascending = False)

Upvotes: -3

Nk03
Nk03

Reputation: 14949

IIUC, you can try:

df = (
    df.sort_values(by='c1', ascending=False)
    .groupby('c2', as_index=False, sort=False)
    .agg(list)
    .explode('c1')
)

Upvotes: 1

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