dataframe - Pandas: Re-assigning values to a 'block' of a Data frame -


probably trivial problem, need understand what's going on here (and how fix it).

suppose have dataframe columns 'a' , 'b', follows:

f = pandas.dataframe({'a':[1,2,3,4,5], 'b':[10,20,30,40,50]})

now every element of 'a' 3 or less, want divide corresponding elements of 'b' 10. 

f[f['a']<=3]['b'] = (f[f['a']<=3]['b'])/10

so values in column 'b' should [1,2,3,40,50].

but find column 'b' remains unchanged! gives?

i think trying assign values copy rather view (f[f['a']<=3]['b'] copy), see returning view versus copy.

however, can reorder , it'll work view:

in [11]: f['b'][f['a']<=3] = (f[f['a']<=3]['b'])/10  in [12]: f out[12]:      b 0  1   1 1  2   2 2  3   3 3  4  40 4  5  50

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