Abbreviate Strings

Description

Abbreviate strings to at least minlength characters, such that they remain unique (if they were), unless strict = TRUE.

Usage

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abbreviate(names.arg, minlength = 4, use.classes = TRUE,
           dot = FALSE, strict = FALSE,
           method = c("left.kept", "both.sides"), named = TRUE)

Arguments

names.arg

a character vector of names to be abbreviated, or an object to be coerced to a character vector by as.character.

minlength

the minimum length of the abbreviations.

use.classes

logical: should lowercase characters be removed first?

dot

logical: should a dot (".") be appended?

strict

logical: should minlength be observed strictly? Note that setting strict = TRUE may return non-unique strings.

method

a character string specifying the method used with default "left.kept", see ‘Details’ below. Partial matches allowed.

named

logical: should names (with original vector) be returned.

Details

The default algorithm (method = "left.kept") used is similar to that of S. For a single string it works as follows. First spaces at the ends of the string are stripped. Then (if necessary) any other spaces are stripped. Next, lower case vowels are removed followed by lower case consonants. Finally if the abbreviation is still longer than minlength upper case letters and symbols are stripped.

Characters are always stripped from the end of the strings first. If an element of names.arg contains more than one word (words are separated by spaces) then at least one letter from each word will be retained.

Missing (NA) values are unaltered.

If use.classes is FALSE then the only distinction is to be between letters and space.

Value

A character vector containing abbreviations for the character strings in its first argument. Duplicates in the original names.arg will be given identical abbreviations. If any non-duplicated elements have the same minlength abbreviations then, if method = "both.sides" the basic internal abbreviate() algorithm is applied to the characterwise reversed strings; if there are still duplicated abbreviations and if strict = FALSE as by default, minlength is incremented by one and new abbreviations are found for those elements only. This process is repeated until all unique elements of names.arg have unique abbreviations.

If names is true, the character version of names.arg is attached to the returned value as a names attribute: no other attributes are retained.

If a input element contains non-ASCII characters, the corresponding value will be in UTF-8 and marked as such (see Encoding).

Warning

If use.classes is true (the default), this is really only suitable for English, and prior to R 3.3.0 did not work correctly with non-ASCII characters in multibyte locales. It will warn if used with non-ASCII characters (and required to reduce the length).

As from R 3.3.0 the concept of ‘vowel’ is extended from English vowels by including characters which are accented versions of lower-case English vowels (including ‘o with stroke’). Of course, there are languages (even Western European languages such as Welsh) with other vowels.

See Also

substr.

Examples

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x <- c("abcd", "efgh", "abce")
abbreviate(x, 2)
abbreviate(x, 2, strict = TRUE) # >> 1st and 3rd are == "ab"

(st.abb <- abbreviate(state.name, 2))
stopifnot(identical(unname(st.abb),
           abbreviate(state.name, 2, named=FALSE)))
table(nchar(st.abb)) # out of 50, 3 need 4 letters :
as <- abbreviate(state.name, 3, strict = TRUE)
as[which(as == "Mss")]

## and without distinguishing vowels:
st.abb2 <- abbreviate(state.name, 2, FALSE)
cbind(st.abb, st.abb2)[st.abb2 != st.abb, ]

## method = "both.sides" helps:  no 4-letters, and only 4 3-letters:
st.ab2 <- abbreviate(state.name, 2, method = "both")
table(nchar(st.ab2))
## Compare the two methods:
cbind(st.abb, st.ab2)

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