Names Attribute in

About Names Attribute

Vectors can have named elements, which sometimes makes them more convenient to work with.

Creation

There are three ways to add names to a vector.

1. At vector creation time

> work_days <- c(Mon = TRUE, Tue = TRUE, Wed = TRUE, Thu = TRUE, Fri = TRUE, Sat = FALSE, Sun = FALSE)
> work_days
  Mon   Tue   Wed   Thu   Fri   Sat   Sun 
 TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE 

1. By assigning a character vector to names()

> months <- c(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)
> names(months) <- month.abb
> months
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 
 31  28  31  30  31  30  31  31  30  31  30  31 

1. With setNames()

> months <- c(31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31)
> setNames(months, month.name)
  January  February     March     April       May      June      July    August September   October  November  December 
       31        28        31        30        31        30        31        31        30        31        30        31 

Removal

If names are no longer wanted they can be removed by setting to NULL

> work_days
  Mon   Tue   Wed   Thu   Fri   Sat   Sun 
 TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE 
> names(work_days) <- NULL
> work_days
[1]  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE

The unname() function achieves the same thing, and perhaps make your intention clearer.

Working with names

The names() function can retrieve names as well as set them.

> names(months) <- month.abb
> names(months)[1:3]
[1] "Jan" "Feb" "Mar"

A name can be used in place of the position index, with quotes required in this case.

> months[c("Jul", "Aug")]
Jul Aug 
 31  31 

For such indexing to work correctly, it is best to ensure that names are unique and non-missing. However, R does not enforce uniqueness.

The usual vector operations still work, and names usually will be preserved if that makes sense.

> months[months == 30]
Apr Jun Sep Nov 
 30  30  30  30 

> sum(months)
[1] 365  # no meaningful names possible

More advanced topics

Many R objects, including vectors, can have arbitrary attributes attached to them. The names attribute is just one example, though a particularly common and important one.

In practice, names are sometimes useful for vectors but rarely essential. The names-attribute becomes much more important for more complex structures such as lists and dataframes, as we shall see in future concepts.