R Language Creating vectors Creating named vectors
Example
Named vector can be created in several ways. With c:
xc <- c('a' = 5, 'b' = 6, 'c' = 7, 'd' = 8)
which results in:
> xc
a b c d
5 6 7 8
with list:
xl <- list('a' = 5, 'b' = 6, 'c' = 7, 'd' = 8)
which results in:
> xl
$a
[1] 5
$b
[1] 6
$c
[1] 7
$d
[1] 8
With the setNames function, two vectors of the same length can be used to create a named vector:
x <- 5:8
y <- letters[1:4]
xy <- setNames(x, y)
which results in a named integer vector:
> xy
a b c d
5 6 7 8
As can be seen, this gives the same result as the c method.
You may also use the names function to get the same result:
xy <- 5:8
names(xy) <- letters[1:4]
With such a vector it is also possibly to select elements by name:
> xy["c"]
c
7
This feature makes it possible to use such a named vector as a look-up vector/table to match the values to values of another vector or column in dataframe. Considering the following dataframe:
mydf <- data.frame(let = c('c','a','b','d'))
> mydf
let
1 c
2 a
3 b
4 d
Suppose you want to create a new variable in the mydf dataframe called num with the correct values from xy in the rows. Using the match function the appropriate values from xy can be selected:
mydf$num <- xy[match(mydf$let, names(xy))]
which results in:
> mydf
let num
1 c 7
2 a 5
3 b 6
4 d 8
