How to delete multiple values from a vector?

Question

The %in% operator tells you which elements are among the numers to remove:

> a <- sample (1 : 10)
> remove <- c (2, 3, 5)
> a
 [1] 10  5  2  7  1  6  3  4  8  9
> a %in% remove
 [1] FALSE  TRUE  TRUE FALSE FALSE FALSE  TRUE FALSE FALSE FALSE
> a [! a %in% remove]
 [1] 10  7  1  6  4  8  9

Note that this will silently remove incomparables (stuff like NA or Inf) as well (while it will keep duplicate values in a as long as they are not listed in remove).

• If a can contain incomparables, but remove will not, we can use match, telling it to return 0 for non-matches and incomparables (%in% is a conventient shortcut for match):

  > a <- c (a, NA, Inf)
  > a
   [1]  10   5   2   7   1   6   3   4   8   9  NA Inf
  > match (a, remove, nomatch = 0L, incomparables = 0L)
   [1] 0 3 1 0 0 0 2 0 0 0 0 0
  > a [match (a, remove, nomatch = 0L, incomparables = 0L) == 0L]
  [1]  10   7   1   6   4   8   9  NA Inf
  

  incomparables = 0 is not needed as incomparables will anyways not match, but I'd include it for the sake of readability.
  This is, btw., what setdiff does internally (but without the unique to throw away duplicates in a which are not in remove).

• If remove contains incomparables, you'll have to check for them individually, e.g.

  if (any (is.na (remove))) 
    a <- a [! is.na (a)]
  

  (This does not distinguish NA from NaN but the R manual anyways warns that one should not rely on having a difference between them)

  For Inf/ -Inf you'll have to check both sign and is.finite

You can use setdiff.

Given

a <- sample(1:10)
remove <- c(2, 3, 5)

Then

> a
 [1] 10  8  9  1  3  4  6  7  2  5
> setdiff(a, remove)
[1] 10  8  9  1  4  6  7

You can do it as follows:

> x<-c(2, 4, 6, 9, 10) # the list
> y<-c(4, 9, 10) # values to be removed

> idx = which(x %in% y ) # Positions of the values of y in x
> idx
[1] 2 4 5
> x = x[-idx] # Remove those values using their position and "-" operator
> x
[1] 2 6

Shortly

> x = x[ - which(x %in% y)]

instead of

x <- x[! x %in% c(2,3,5)]

using the packages purrr and magrittr, you can do:

your_vector %<>% discard(~ .x %in% c(2,3,5))

this allows for subsetting using the vector name only once. And you can use it in pipes :)

First we can define a new operator,

"%ni%" = Negate( "%in%" )

Then, its like x not in remove

x <- 1:10
remove <- c(2,3,5)
x <- x[ x %ni% remove ]

or why to go for remove, go directly

x <- x[ x %ni% c(2,3,5)]

There is also subset which might be useful sometimes:

a <- sample(1:10)
bad <- c(2, 3, 5)

> subset(a, !(a %in% bad))
[1]  9  7 10  6  8  1  4