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Last data update: 2014.03.03

R: Extract and replace substrings from a character vector.

str_sub

R Documentation

Extract and replace substrings from a character vector.

Description

str_sub will recycle all arguments to be the same length as the longest argument. If any arguments are of length 0, the output will be a zero length character vector.

Usage

str_sub(string, start = 1L, end = -1L)

str_sub(string, start = 1L, end = -1L) <- value

Arguments

string

input character vector.

start,end

Two integer vectors. start gives the position of the first character (defaults to first), end gives the position of the last (defaults to last character). Alternatively, pass a two-column matrix to start.

Negative values count backwards from the last character.

value

replacement string

Details

Substrings are inclusive - they include the characters at both start and end positions. str_sub(string, 1, -1) will return the complete substring, from the first character to the last.

Value

A character vector of substring from start to end (inclusive). Will be length of longest input argument.

Examples

hw <- "Hadley Wickham"

str_sub(hw, 1, 6)
str_sub(hw, end = 6)
str_sub(hw, 8, 14)
str_sub(hw, 8)
str_sub(hw, c(1, 8), c(6, 14))

# Negative indices
str_sub(hw, -1)
str_sub(hw, -7)
str_sub(hw, end = -7)

# Alternatively, you can pass in a two colum matrix, as in the
# output from str_locate_all
pos <- str_locate_all(hw, "[aeio]")[[1]]
str_sub(hw, pos)
str_sub(hw, pos[, 1], pos[, 2])

# Vectorisation
str_sub(hw, seq_len(str_length(hw)))
str_sub(hw, end = seq_len(str_length(hw)))

# Replacement form
x <- "BBCDEF"
str_sub(x, 1, 1) <- "A"; x
str_sub(x, -1, -1) <- "K"; x
str_sub(x, -2, -2) <- "GHIJ"; x
str_sub(x, 2, -2) <- ""; x