Partially replace regex pattern in string using gsub in R?

Question

I have to replace " used as a unit of measure (inches) in strings that also contain characters in double quotes.

uuuu<- c('BELT, "V" 5L610, LONG 4.5" WIDE 7.5", TYPE "K"')

The vector in my data has 70k+ rows, I only need to worry about the " right after numbers. my desired results would be - BELT, "V" 5L610, LONG 4.5IN WIDE 7.5IN, TYPE "K"

I tried gsub('\\d\"',"\\dIN",uuuu) but you know that's not going to give me the result correct result: "BELT, \"V\" 5L610, LONG 4.dIN WIDE 7.dIN, TYPE \"K\"

Then I tried grep to find the pattern and get the indices, however, that doesn't seem to reasonable since a single string in the vector could have both " as a UOM and as a quote. grep('\\d\"',uuuu,value = FALSE)

How do I retain the digit from my pattern? It should be possible in gsub?

@WiktorStribiżew Thank you, I have come across 1,2 before in Regex. But I was not able to find a reference where I can learn about exactly what they are? can you share a reference? If you want I'll the accept the solution if posted. — pyeR_biz
– pyeR_biz, Commented Jan 20, 2018 at 20:49

Wiktor Stribiżew · Accepted Answer · 2018-01-21 09:44:54Z

2

You may use a capturing group (a pair of unescaped parentheses) around the part of the pattern you need to keep after replacement and a backreference to the group value inside the replacement pattern:

gsub('(\\d)"', "\\1IN", uuuu)
      ^   ^     ^^^

See the regex demo.

Pattern details

(\d) - Capturing group 1 (whose value can be referenced to with a \1 backreference from the replacement pattern): any digit
" - a double quote.

R demo:

uuuu<- c('BELT, "V" 5L610, LONG 4.5" WIDE 7.5", TYPE "K"')
cat(gsub('(\\d)"', "\\1IN", uuuu))
## => BELT, "V" 5L610, LONG 4.5IN WIDE 7.5IN, TYPE "K"

answered Jan 21, 2018 at 9:44

Wiktor Stribiżew

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