[R] difference between <- and =
Richard A. O'Keefe
ok at cs.otago.ac.nz
Tue Sep 2 01:18:43 CEST 2003
Spencer Graves <spencer.graves at PDF.COM> wrote:
A common, punishing error for me, with DF being a data frame, is the
if(DF$a = 1) ...
where I intended to write "if(DF$a == 1)...".
This is a syntax error in R.
> d <- data.frame(a=2,b=3,c=4)
> if (d$a=1) cat("foo!")
Error: syntax error
If I've understood the R documentation correctly, "=" is only allowed
as a synonym for "<-" at "statement" level.
Of course, that's one more reason not to use "=" when you DO want
assignment; "<-" has no such restriction.
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