startsWith

R Base 3.6.2

Determines if entries of x start or end with string (entries of) prefix or suffix respectively, where strings are recycled to common lengths. startsWith() is equivalent to but much faster thansubstring(x, 1, nchar(prefix)) == prefixor alsogrepl("^", x)where prefix is not to contain special regular expression characters.

Syntax

startsWith(x, prefix)
  endsWith(x, suffix)

Arguments

Parameter	Description
`x`	vector of character string whose “starts” are considered.
`prefix, suffix`	character vector (often of length one).

Return Value

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.

Details

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.

Examples

Example

# NOT RUN {
startsWith(search(), "package:") # typically at least two FALSE, nowadays often three

x1 <- c("Foobar", "bla bla", "something", "another", "blu", "brown",
        "blau bl<U+00FC>ht 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
# }