str_sub: Extract and replace substrings from a character vector

In csdaw/stringrb: A Base R Version of 'stringr'

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 = 1000000L)

str_sub(string, start = 1L, end = 1000000L, omit_na = FALSE) <- value

Arguments

string	character vector of strings.
start	integer vector giving the position(s) of the first character, default is 1L. Negative values count backwards from the last character. Alternatively pass a two-column numeric matrix e.g. the output of str_locate_all().
end	integer vector giving the position(s) of the last character, default is 1000000L. Negative values count backwards from the last character.
omit_na	logical, default is FALSE, If TRUE, missing values in any of the arguments provided will result in an unchanged input.
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.

This function includes limited support for replacement form. Substring length must match replacement length only one replacement can be made per string. For multiple replacements per string it is probably better to use mgsub() from the mgsub package.

Value

Returns a character vector of substring(s) from start to end (inclusive). Will be the 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 column 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(nchar(hw)))
str_sub(hw, end = seq_len(nchar(hw)))

# Replacement form
# (Limited support, substring length must match replacement length and
# only one replacement can be made per string.)
test <- c("red", "orange", "green", "blue")
str_sub(test, 1, 3) <- "333"
test

test2 <- c("Africa", "Asia", "Australia")
str_sub(test2, -2) <- "z"
test2

# If you want to keep the original string if some argument is NA,
# use omit_na = TRUE

x1 <- x2 <- x3 <- x4 <- "AAA"
str_sub(x1, 1, NA) <- "B"
str_sub(x2, 1, 2) <- NA
str_sub(x3, 1, NA, omit_na = TRUE) <- "B"
str_sub(x4, 1, 2, omit_na = TRUE) <- NA
x1; x2; x3; x4

csdaw/stringrb documentation built on Aug. 13, 2022, 10:55 p.m.