CODEWITHSUNDEEP
rregexgsub
I am Nik
I am Nik

Reputation: 129

Regex to replace comma to dot separator

I am trying to replace comma separator to a dot separator (and vice versa) in numbers, while lines may have other dots and commas. I tried using gsub(), but don't know how to stop it from recognizing replacement pattern as a character string.

For example, suppose I have a line

`Today I bought apples, oranges for 3,55 dollars`

where I want to replace comma separator to a dot separator at the price:

`Today I bought apples, oranges for 3.55 dollars`

A naive gsub approach doesnt work as I want to:

`gsub('[[:digit:]],[[:digit:]]',
      '[[:digit:]][.][[:digit:]]',
      'Today I bought apples, oranges for 3,55 dollars')`

which obviously gives [1] "Today I bought apples, oranges for [[:digit:]][.][[:digit:]]5 dollars", i.e. gsub treats the replacement as a character line.

I cannot supply anything other than a string to gsub(). What can I do then? I have in mind that maybe I can write a function that will match this pattern, then basically replace , to . inside this pattern and place it back in the sentence. However, I hope there is a shorter solution for such a problem. Any ideas?

Upvotes: 0

Views: 1502

Answers (3)

talat
talat

Reputation: 70336

You can use capture groups and reference them in the replacement:

gsub("(\\d+),(\\d+)", "\\1.\\2", "Today I bought apples, oranges for 3,55 dollars")

# [1] "Today I bought apples, oranges for 3.55 dollars"

Upvotes: 3

jasbner
jasbner

Reputation: 2283

You can group each digit with parenthesis and recall them in the second part of the substitution. Below \\1 recalls the first set of parenthesis and \\2 the second set. 

gsub('([[:digit:]]),([[:digit:]])','\\1.\\2','Today I bought apples, oranges for 3,55 dollars')
# [1] "Today I bought apples, oranges for 3.55 dollars"

Upvotes: 1

akrun
akrun

Reputation: 887951

We can use a regex lookaround to match the , before a numeric and a numeric value and replace it with .

gsub("(?<=[0-9]),(?=[0-9])", ".", str1, perl = TRUE)
#[1] "Today I bought apples, oranges for 3.55 dollars"

data

str1 <- 'Today I bought apples, oranges for 3,55 dollars'

Upvotes: 2

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