# stri_sub

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##### Extract a Substring From or Replace a Substring In a Character Vector

The first function extracts substrings under code point-based index ranges provided. The second one allows to substitute parts of a string with given strings.

##### Usage
stri_sub(str, from = 1L, to = -1L, length)
stri_sub(str, from = 1L, to = -1L, length, omit_na=FALSE) <- value<="" div="">
##### Arguments
str
character vector
from
integer vector or two-column matrix
to
integer vector; mutually exclusive with length and from being a matrix
length
integer vector; mutually exclusive with to and from being a matrix
omit_na
single logical value; if TRUE, missing values in from, to, or length will result in an unchanged input; replacement function only
value
character vector to be substituted with; replacement function only
##### Details

Vectorized over str, [value], from and (to or length). to and length are mutually exclusive.
to has priority over length. If from is a two-column matrix, then the first column is used as from and the second one as to. In such case arguments to and length are ignored.
Of course, the indices are code point-based, and not byte-based. Note that for some Unicode strings, the extracted substrings may not be well-formed, especially if the input is not NFC-normalized (see stri_trans_nfc), includes byte order marks, Bidirectional text marks, and so on. Handle with care.
Indices are 1-based, i.e., an index equal to 1 denotes the first character in a string, which gives a typical R look-and-feel. Argument to defines the last index of the substring, inclusive.
For negative indices in from or to, counting starts at the end of the string. For instance, index -1 denotes the last code point in the string. Negative length means counting backwards.
In stri_sub, out-of-bound indices are silently corrected. If from > to, then an empty string is returned.
In stri_sub<-< code="">, some configurations of indices may work as string concatenation at the front, back, or middle. 

##### Value

stri_sub returns a character vector. stri_sub<-< code=""> changes the str object.The extract function stri_sub returns the indicated substrings. The replacement function stri_sub<-< code=""> is invoked for its side effect: after a call, str is modified. 

Other indexing: stri_locate_all_boundaries, stri_locate_all
library(stringi) s <- "Lorem ipsum dolor sit amet, consectetur adipisicing elit." stri_sub(s, from=1:3*6, to=21) stri_sub(s, from=c(1,7,13), length=5) stri_sub(s, from=1, length=1:3) stri_sub(s, -17, -7) stri_sub(s, -5, length=4) (stri_sub(s, 1, 5) <- "stringi") (stri_sub(s, -6, length=5) <- ".") (stri_sub(s, 1, 1:3) <- 1:2) x <- c("a;b", "c:d") (stri_sub(x, stri_locate_first_fixed(x, ";"), omit_na=TRUE) <- "_")