what is wrong with this pandas expression

Question

I'm new to Pandas, the answer may be obvious.

I have 3 series of the same length: a, b, c

a[b > c] = 0

works, but:

a[math.fabs(b) > c] = 0

doesn't work, and

a[(b > c or b < -c)] = 0

doesn't work either.

How can I implement that logic?

`a[(b>c) | (b<-c)]` or `a[b.abs().gt(c)]`? Make sure that `a,b,c` are not just equal length, they should have same indexing as well. — Quang Hoang, Jul 22 '19 at 20:33
Please have a look at [How to create good pandas examples](https://stackoverflow.com/questions/20109391/how-to-make-good-reproducible-pandas-examples) and provide a [mcve] for your issue so that we can provide more specific help — G. Anderson, Jul 22 '19 at 20:34
What do you mean by "it doesn't work"? Do you get an error? Do you get unexpected results? — John Gordon, Jul 22 '19 at 20:36
On your third example, see [this answer](https://stackoverflow.com/questions/21415661/logical-operators-for-boolean-indexing-in-pandas). — Brendan, Jul 22 '19 at 20:51
@JohnGordon, sorry I should have written the error: : (, ValueError('The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().'), None) — Thomas, Jul 22 '19 at 21:39

score -1 · Answer 1 · edited Aug 16 '19 at 20:57

Your issue is that in the first expression the expression you use is vectorized while in the other one it is not.

In the first expression, the < operation between two series returns a series as well
In the second expression, math.fabs is supposed to be applied elements by elements and not to an array/series of elements (try the numpy version instead is it exists).
In the third expression, the or operation is not vectorized and you should use | instead.

1 Answers1