I'm using R 2.8.1 and it is possible to use both = and <- as variable assignment operators. What's the difference between them? Which one should I use?
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A:
From here:
The operators <- and = assign into the environment in which they are evaluated. The operator <- can be used anywhere, whereas the operator = is only allowed at the top level (e.g., in the complete expression typed at the command prompt) or as one of the subexpressions in a braced list of expressions.
Mark Byers
2010-02-16 08:56:55
As `<-` can be used anywhere, does this mean that there is no need to use `=` ?
Mehper C. Palavuzlar
2010-02-16 09:00:38
No, you need to still need to use `=` when calling functions to avoid assigning globally. Look at these examples: http://www.mayin.org/ajayshah/KB/R/html/b1.html. If you used `name<-"paypal", x<-2, ...` it would set `x` at the top level. Try running that example but writing `<-` instead of `=` and see what happens.
Mark Byers
2010-02-16 09:07:06
Oh I see now... Thanks for your help.
Mehper C. Palavuzlar
2010-02-16 09:14:04
+5
A:
Reading from "Introducing Monte Carlo Methods with R", by Robert and Casella:
"The assignment operator is =, not to be confused with ==, which is the Boolean operator for equality. An older assignment operator is <- and, for compatibility reasons, it still remains functional, but it should be ignored to ensure cleaner programming.
(As pointed out by Spector, P. (2009). 'Data Manipulation with R' - Section 8.7., an exception is when using system.time, since = is then used to identify keywords)
A misleading feature of the assignment operator <- is found in Boolean expressions such as
> if (x[1]<-2) ...
which is supposed to test whether or not x[1] is less than -2 but ends up allocating 2 to x[1], erasing its current value! Note also that using
> if (x[1]=-2) ...
mistakenly instead of (x[1]==-2) has the same consequence."
gd047
2010-02-16 09:53:35
I also think that `global assignment`, whatever the need for doing something like this, can only be performed using the ("gets"-based) `<<-` operator, and that there is not an "equals"-based equivalent.
gd047
2010-02-16 14:59:41
Google's R style guide says the opposite: http://google-styleguide.googlecode.com/svn/trunk/google-r-style.html#assignment
Mark Byers
2010-08-08 09:52:37