API/ENH: enable boolean indexing conditions to reference its input frame via eval

[jreback]

http://stackoverflow.com/questions/19938734/is-there-a-simple-way-to-reference-the-current-object-after-applying-a-chain-of

df.where("A>0",1)
df.loc["A>0"]

so could process the condition via an 'eval' type of operation

[jreback]

@cpcloud might be interesting

[jonblunt]

When I posted on stackoverflow I was thinking of a "magic" character/name that would stand for the parent object.

eg
ts.where( '_ > 0 )

having '_'stand for the object upon which the method is called. Often in my usage the object is an unnamed series.

The eval syntax works when the calling object is a DataFrame and the columns have names that can be intuited from the previous action, but an unnamed series has no name.

[cpcloud]

I seem to be missing these kinds of things....guess I should look at the "mentioning you" more often... @jreback sorry about that

[jreback]

ha! though I think needs some thinking about

[cpcloud]

@jreback what do u think about the _ idea from @jonblunt? i think u could just pass to query and have _ mean self, no?

[jreback]

sure but then I'll bet people would want it for regular usage (non query/eval)

prob a reasonable idea though

[cpcloud]

oh i c now u wanted to have string input used in query and whatever the query was eval it on the caller

[cpcloud]

but that happens anyway ... you can chain as much as you want, but you must refer to either cols or locals

[jreback]

hmm, can now do this by using .assign (as an input to .query), though not explicity supported in eval

[jreback]

closed by #12539