Does String Start or End With Another String?

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Description

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 than

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substring(x, 1, nchar(prefix)) == prefix

or also

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grepl("^<prefix>", x)

where prefix is not to contain special regular expression characters.

Usage

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

Arguments

x

vector of character string whose “starts” are considered.

prefix, suffix

character vector (often of length one).

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.

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.

See Also

grepl, substring; the partial string matching functions charmatch and pmatch solve a different task.

Examples

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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

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