问题
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Assignment operators in R: '=' and '<-'
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?
回答1:
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.
回答2:
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."
来源：https://stackoverflow.com/questions/2271575/whats-the-difference-between-and-in-r