What's the difference between `=` and `<-` in R?
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.
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."