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38 lines
1.3 KiB
R
38 lines
1.3 KiB
R
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#' Extract string based on regex pattern
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#'
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#' Use base::strsplit to
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#' @param d vector of character strings
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#' @param pattern regex pattern to match
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#'
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#' @return vector of character strings
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#' @export
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#'
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#' @examples
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#' ls <- do.call(c,lapply(sample(4:8,20,TRUE),function(i){
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#' paste(sample(letters,i,TRUE),collapse = "")}))
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#' ds <- do.call(c,lapply(1:20,function(i){
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#' paste(sample(ls,1),i,sample(ls,1),"23",sep = "_")}))
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#' str_extract(ds,"([0-9]+)")
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str_extract <- function(d,pattern){
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if (!is.vector(d)) stop("Please provide a vector")
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## Drawing on the solution in REDCapCAST::strsplitx to split around pattern
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nl <- strsplit(gsub("~~", "~", # Removes double ~
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gsub("^~", "", # Removes leading ~
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gsub(
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# Splits and inserts ~ at all delimiters
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paste0("(", pattern, ")"), "~\\1~", d
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))), "~")
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## Reusing the pattern, to sub with "" and match on length 0 to index the
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## element containing the pattern. Only first occurance included.
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indx <- lapply(nl,function(i){
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match(0,nchar(sub(pattern,"",i)))
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})
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## Using lapply to subsset the given index for each element in list
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do.call(c,lapply(seq_along(nl), function(i){
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nl[[i]][indx[[i]]]
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} ))
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}
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