Re: [igraph] iterator selections and logic short-circuiting

[Gábor Csárdi]

Carl,

just a comment. I think the expression

E(g)[!a && b]

does not make much sense, because '&&' is _not_ an element-wise operator. E.g.:

    a <- c(FALSE, TRUE, TRUE)
    b <- c(FALSE, FALSE, TRUE)
    a && b
    # [1] FALSE
    a & b
    # [1] FALSE FALSE  TRUE

'&&' is actually only evaluates the second argument is the first one
evaluates to TRUE.

Best,
Gabor

On Tue, Sep 11, 2012 at 11:30 AM, Carl Pearson <address@hidden> wrote:
> Using the iterator function, with a logical query
>
> E(g)[!a && b]
>
> is causing complaints when '!a' evaluates FALSE (i.e., the expression
> should be short-circuited) and 'b' is null.  I'm working around this
> currently, but this struck me as indicating an opportunity to trim
> some unnecessary operations under the iterator hood (no clue how it
> actually works, however, so can't suggest anything).
>
> Also, provided there isn't some gross performance trade, clearly I'd
> like to use the iterator query this way.
>
> C
>
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-- 
Gabor Csardi <address@hidden>     MTA KFKI RMKI