simplify replace ops

[moodymudskipper]

replace ops are built around x <- replace(x, cond, value) with specific cases for

• factors
• when the condition is never met.

I'm questioning both special cases.

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First case was to counter this :

x <- factor(letters[1:3])
x[x == "b"] <- "Z"
#> Warning in `[<-.factor`(`*tmp*`, x == "b", value = "Z"): niveau de facteur
#> incorrect, NAs générés
x
#> [1] a    <NA> c   
#> Levels: a b c

so x == "b" <- "Z" would replace the levels smoothly.

I think it might have been a bad idea as we could simply do : levels(x) == "b" <- "Z" in that case with more consistency and less ambiguity in some corner cases.

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Special case for when the condition was never met was designed so the following wouldn't alter x :

x <- 1:3
x < 0 <- "a"

but now I think it's good that x[x <0] <- "a" coerces to character even if the condition is never met, because of type stability. and our assignment functions would be more intuitive if they were all really simple shortcuts for cond(x) <- value equivalent to x[cond(x)] <- value.

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@KKPMW do you see a problem with simplifying those ?

[karoliskoncevicius]

I agree with both of the points 100%. Unless I missed some corner case.

[moodymudskipper]

done with 19f10f9