From Kurt@Horn|k @end|ng |rom wu@@c@@t  Thu Sep  9 09:23:24 2021
From: Kurt@Horn|k @end|ng |rom wu@@c@@t (Kurt Hornik)
Date: Thu, 9 Sep 2021 09:23:24 +0200
Subject: [Rd] Should Position() use match.fun()?
In-Reply-To: <CAP=dwz9FY4j77S0Qm+grtX+S=Hjud6UF5+csewX6J4mG2HUHnQ@mail.gmail.com>
References: <CAP=dwz9FY4j77S0Qm+grtX+S=Hjud6UF5+csewX6J4mG2HUHnQ@mail.gmail.com>
Message-ID: <24889.46700.99366.498401@hornik.net>

>>>>> Steve Martin writes:

> Hello,
> All of the funprog functions except Position() use match.fun() early
> in the body of the function. (Filter() seems to rely on lapply() for
> this, but the effect is the same.) 

Right. 

> In most cases this isn't a problem, but I can't see why Position()
> shouldn't look something like

> Position2 <- function(f, x, right = FALSE, nomatch = NA_integer_) {
>     f <- match.fun(f) # the only difference from Position()
>     ind <- if (right) rev(seq_along(x)) else seq_along(x)
>     for (i in ind) {
>         if (f(x[[i]])) return(i)
>     }
>     nomatch
> }

> This would make it consistent with the other funprog functions, and
> would mean that Find() and Position() give the same result when
> expected

Indeed.  I'll look into adding the match.fun ...

Best
-k

>> equals3 <- function(x) x == 3
>> Position("equals3", 1:5)
> Error in f(x[[i]]) : could not find function "f"
>> Position2("equals3", 1:5)
> [1] 3
>> Find("equals3", 1:5)
> [1] 3

> Thanks,
> Steve

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[Rd] Should Position() use match.fun()?
Kurt Hornik