unique

R Base 3.6.2

unique returns a vector, data frame or array like x but with duplicate elements/rows removed.

Syntax

unique(x, incomparables = FALSE, &#8230;)<p></p><p># S3 method for default
unique(x, incomparables = FALSE, fromLast = FALSE,
        nmax = NA, &#8230;)</p><p># S3 method for matrix
unique(x, incomparables = FALSE, MARGIN = 1,
       fromLast = FALSE, &#8230;)</p><p># S3 method for array
unique(x, incomparables = FALSE, MARGIN = 1,
       fromLast = FALSE, &#8230;)</p>

Arguments

Parameter	Description
`x`	a vector or a data frame or an array or NULL.
`incomparables`	a vector of values that cannot be compared. FALSE is a special value, meaning that all values can be compared, and may be the only value accepted for methods other than the default. It will be coerced internally to the same type as x.
`fromLast`	logical indicating if duplication should be considered from the last, i.e., the last (or rightmost) of identical elements will be kept. This only matters for names or dimnames.
`nmax`	the maximum number of unique items expected (greater than one). See duplicated.
`…`	arguments for particular methods.
`MARGIN`	the array margin to be held fixed: a single integer.

Return Value

For a vector, an object of the same type of x, but with only one copy of each duplicated element. No attributes are copied (so the result has no names). For a data frame, a data frame is returned with the same columns but possibly fewer rows (and with row names from the first occurrences of the unique rows). A matrix or array is subsetted by [, drop = FALSE], so dimensions and dimnames are copied appropriately, and the result always has the same number of dimensions as x.

Details

This is a generic function with methods for vectors, data frames and arrays (including matrices). The array method calculates for each element of the dimension specified by MARGIN if the remaining dimensions are identical to those for an earlier element (in row-major order). This would most commonly be used for matrices to find unique rows (the default) or columns (with MARGIN = 2). Note that unlike the Unix command uniq this omits duplicated and not just repeated elements/rows. That is, an element is omitted if it is equal to any previous element and not just if it is equal the immediately previous one. (For the latter, see rle). Missing values ("NA") are regarded as equal, numeric and complex ones differing from NaN; character strings will be compared in a “common encoding”; for details,

Examples

Example

# NOT RUN {
x <- c(3:5, 11:8, 8 + 0:5)
(ux <- unique(x))
(u2 <- unique(x, fromLast = TRUE)) # different order
stopifnot(identical(sort(ux), sort(u2)))

length(unique(sample(100, 100, replace = TRUE)))
## approximately 100(1 - 1/e) = 63.21

unique(iris)
# }