| startsWith | R Documentation |
Determines if entries of x start or end with string (entries of)
prefix or suffix respectively, where strings are
recycled to common lengths.
startsWith(x, prefix) endsWith(x, suffix)
x |
vector of |
prefix, suffix |
|
startsWith() is equivalent to but much faster than
substring(x, 1, nchar(prefix)) == prefix
or also
grepl("^<prefix>", x)
where prefix is not to contain special regular expression
characters (and for grepl, x does not contain missing
values, see below).
The code has an optimized branch for the most common usage in which
prefix or suffix is of length one, and is further
optimized in a UTF-8 or 8-byte locale if that is an ASCII string.
A logical vector, of “common length” of x
and prefix (or suffix), i.e., of the longer of the two
lengths unless one of them is zero when the result is
also of zero length. A shorter input is recycled to the output length.
grepl, substring; the partial string
matching functions charmatch and pmatch
solve a different task.
startsWith(search(), "package:") # typically at least two FALSE, nowadays often three
x1 <- c("Foobar", "bla bla", "something", "another", "blu", "brown",
"blau blüht der Enzian")# non-ASCII
x2 <- cbind(
startsWith(x1, "b"),
startsWith(x1, "bl"),
startsWith(x1, "bla"),
endsWith(x1, "n"),
endsWith(x1, "an"))
rownames(x2) <- x1; colnames(x2) <- c("b", "b1", "bla", "n", "an")
x2
## Non-equivalence in case of missing values in 'x', see Details:
x <- c("all", "but", NA_character_)
cbind(startsWith(x, "a"),
substring(x, 1L, 1L) == "a",
grepl("^a", x))
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