Pandas 'isin' with output keeping order of input list

Question

When I have a dataframe

df = DataFrame({'A': [5, 6, 3, 4], 'B': [1, 2, 3, 5]})
df

   A  B
0  5  1
1  6  2
2  3  3
3  4  5

I can use

df[df['A'].isin([3, 6])]

in order to select rows having the passed values.

Is there also a way to keep the order of the input list?

So that my output is not:

   A  B
1  6  2
2  3  3

but

   A  B
1  3  3
2  6  2

Answer 1

This is a bit long, but it works. isin(), then sort_values() based on the list.

df = pandas.DataFrame({'A' : [5,6,3,4], 'B' : [1,2,3,5]})
mylist = [3,6]
ndf =  df[df['A'].isin(mylist)]
ndf['sort_cat'] = pandas.Categorical(ndf['A'], categories=mylist, ordered=True)
ndf.sort_values('sort_cat', inplace=True)
ndf.reset_index(inplace=True)
print ndf
   A  B sort_cat
2  3  3        3
1  6  2        6

(I based this answer on sort pandas dataframe based on list)

Answer 2

Another option which filters and sorts in one shot

import pandas as pd
from functools import reduce
reduce(pd.DataFrame.append, map(lambda i: df[df.A == i], [3, 6]))