How to Create and Assign Named Vectors in R
You use the assignment operator (<-) to assign names to vectors in much the same way that you assign values to character vectors.
Imagine you want to create a named vector with the number of days in each month. First, create a numeric vector containing the number of days in each month. Then use the built-in dataset month.name for the month names, as follows:
> month.days <- c(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31) > names(month.days) <- month.name > month.days January February March April 31 28 31 30 May June July August 31 30 31 31 September October November December 30 31 30 31
Now you can use this vector to find the names of the months with 31 days:
> names(month.days[month.days==31])  "January" "March" "May"  "July" "August" "October"  "December"
This technique works because you subset month.days to return only those values for which month.days equals 31, and then you retrieve the names of the resulting vector.
The double equal sign (==) indicates a test for equality. Make sure not to use the single equal sign (=) for equality testing. Not only will a single equal sign not work, but it can have strange side effects because R interprets a single equal sign as an assignment. In other words, the operator = in many cases is the same as <-.