Usage of local variables

问题

Problem:

How to define local variables within a scope in a r-code.

Example:

In C++ the following example defines a scope, and variables declared within the scope are undefined in outside code.

{
     vector V1 = getVector(1);
     vector V1(= getVector(2);
     double P = inner_product(V1, V2);
     print(P);
}
// the variable V1, V2, P are undefined here!

Note: This code is only to illustrate the idea.

This practice has the advantages of:

Keeping the global namespace clean;
simplifying code;
removing ambiguities, specially when a variable is re-used without initialization.

In R, it seems to me that this notion is only existent inside function definitions. So, in order to reproduce the previous example code, I would need to do something like this:

dummy <- function( ) {
     V1 = c(1,2,3);
     V2 = c(1,2,3);
     P = inner_product(V1, V2);
     print(P);
}
dummy( );
# the variable V1, V2, P are undefined here!

or, in an even more obscure way, declare a anonymous function to prevent the function call:

(function() { 
     V1 = c(1,2,3);
     V2 = c(1,2,3);
     P = inner_product(V1, V2);
     print(P);
})()
# the variable V1, V2, P are undefined here!

Question

Is there a more elegant way to create local variable?

回答1:

Use local. Using your example:

local({ 
     V1 = c(1,2,3);
     V2 = c(1,2,3);
     P = inner_product(V1, V2);
     print(P);
})
# the variable V1, V2, P are undefined here!

回答2:

You can create a new environment where your variable can be defined; this is how the local scope within a function is defined.

You can read more about this here

check the help for environment as well i.e. type in your R console ?environment

来源：https://stackoverflow.com/questions/14793113/usage-of-local-variables

标签

scope