gsubfn (version 0.3-1)

strapply: Apply a function over a string or strings.

Description

Similar to "'gsubfn'" except instead of performing substitutions it returns the output of "'FUN'".

Usage

strapply(X, pattern, FUN = function(x, ...) x, ..., 
   simplify = FALSE, USE.NAMES = FALSE, combine = c)

Arguments

X

list or (atomic) vector of character strings to be used.

pattern

character string containing a regular expression (or character string for "'fixed = TRUE')" to be matched in the given character vector.

FUN

a function, formula or proto object to be applied to each element of "'X'". See discussion in gsubfn.

...

optional arguments to "'gsubfn'".

simplify

logical or function. If logical, should the result be simplified to a vector or matrix, as in "sapply" if possible? If function, that function is applied to the result with each component of the result passe

USE.NAMES

logical; if "'TRUE'" and if "'X'" is character, use "'X'" as 'names' for the result unless it had names already.

combine

multiple results from same string are combined using this function. The default is "c". "list" is another common choice. The default may change to be "list" in the future.

Value

• A list of character strings.

Details

If FUN is a function then for each character string in "X" the pattern is repeatedly matched, each such match along with back references, if any, are passed to the function "FUN" and the output of FUN is returned as a list. If FUN is a formula or proto object then it is interpreted to the way discussed in gsubfn.

See Also

See Also as gsubfn, sapply

Examples

strapply("12;34:56,89,,12", "[0-9]+")

# separate leading digits from rest of string
# creating a 3 column matrix: original string, digits, rest
s <- c("123abc", "12cd34", "1e23")
t(strapply(s, "^([[:digit:]]+)(.*)", c, simplify = TRUE)) 

# same but create data.frame
strapply(s, "^([[:digit:]]+)(.*)", c, simplify = rbind)[[1]]

# running window of 5 characters using 0-lookahead perl regexp
x <- "abcdefghijkl"
strapply(x, "(.)(?=(....))",  paste0, backref = -2, perl = TRUE)[[1]]

# Note difference.  First gives character vector.  Second is the same.
# Third has same elements but is a list.
# Fourth gives list of two character vectors. Fifth is the same.
strapply("a:b c:d", "(.):(.)", c)[[1]]
strapply("a:b c:d", "(.):(.)", list, simplify = unlist) # same

strapply("a:b c:d", "(.):(.)", list)[[1]]

strapply("a:b c:d", "(.):(.)", c, combine = list)[[1]]
strapply("a:b c:d", "(.):(.)", c, combine = list, simplify = c) # same

# find second CPU_SPEED value given lines of config file
Lines <- c("DEVICE = 'PC'", "CPU_SPEED = '1999', '233'")
parms <- strapply(Lines, "[^ ',=]+", c, USE.NAMES = TRUE, 
	simplify = ~ lapply(list(...), "[", -1))
parms$CPU_SPEED[2]

# return first two words in each string
p <- proto(fun = function(this, x) if (count <=2) x)
strapply(c("the brown fox", "the eager beaver"), "\\w+", p)

# convert to chron
library(chron)
x <- c("01/15/2005 23:32:45", "02/27/2005 01:22:30")
x.chron <- strapply(x, "(../../....) (..:..:..)",  chron, backref = -2, 
   simplify = c)