assigning using df.loc and unsorted labels doesn't put values in the right places

[sadruddin]

Using 0.13.1 (gohlke binaries, Win64, using numpy 1.8):

When using .loc, when passing unsorted labels, pandas doesn't assign the values in the designed labels' locations. Example:
df = pandas.DataFrame(index=[3, 5, 4], columns=['A'])
df.loc[[4, 3, 5], 'A'] = [1, 2, 3]
Result is:

Out[30]: 
   A
3  1
5  2
4  3

One would have expected:

Out[30]: 
   A
3  2
5  3
4  1

[jreback]

yep....this slipped thru (was trying to fix another case)..

as a work around you can make the rhs a Series (with the correct indexes)

[jreback]

@sadruddin thanks for the report!

[sadruddin]

And thank you for fixing bugs so quickly!
Side question, doesn't it make sense to release a 0.13.2 rather soon? I would say that this is not really a corner case bug that can wait 3-4 months to be fixed in official releases. What do you think?

[jreback]

this is a corner case
just make the rhs a Series

[sadruddin]

The workaround is clear and simple, not arguing about that, I'm just saying that the likelihood of someone else getting caught by that is not small, especially given that it doesn't raise any error or warning, but just silently misplaces the elements

[jreback]

it's a really small corner case and require that the entire column be replaced
u are welcome to use master of even pull the fix and update your local install your self
your was the first time this bug report was raised

0.14 is the next release Ann is soon

[dieterv77]

I think i ran into a related bug (at least i ran into it with 0.13.1, but seems fixed with master):

import pandas
import numpy as np
x = pandas.DataFrame(np.random.randn(3,3))
y = pandas.DataFrame(np.random.randn(3,3),index=[2,0,1],columns=[0,1,2])
x.ix[y.index,y.columns] = y
print np.linalg.norm(y - x)

this will print a nonzero value, but it shouldn't.
The only workaround i see would be to reindex y, but in the actual application, sometimes y is a submatrix (in which case the bug doesn't trigger).

Just wanted to add this data point, in case it can be used to motivate a 0.13.2 bugfix release.

thanks very much