Delete numbers not dates in R (regex)

Question

I want to remove numbers (integers and floats) from a character vector, preserving dates:

"I'd like to delete numbers like 84 and 0.5 but not dates like 2015"

I would like to get:

"I'd like to delete numbers like and but not dates like 2015"

In English a quick and dirty rule could be: if the number starts with 18, 19, or 20 and has length 4, don't delete.

I asked the same question in Python and the answer was very satisfying (\b(?!(?:18|19|20)\d{2}\b(?!\.\d))\d*\.?).

However, when I pass the same regex to grepl in R:

gsub("[\b(?!(?:18|19|20)\d{2}\b(?!\.\d))\d*\.?]"," ", "I'd like to delete numbers like 84 and 0.5 but not dates like 2015")

I get:

Error: '\d' is an unrecognized escape in character string starting ""\b(?!(?:18|19|20)\d"

Just FYI: In R gsub, you need to double backslashes. And you should not put all into a character class [...]. Also, the lookahead requires the use of perl=T. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jan 5, 2016 at 11:23
replace \ with \\. @stribizhev not only for gsub.. And also don't put your regex inside []. — Avinash Raj
– Avinash Raj, Commented Jan 5, 2016 at 11:23
Use gsub("\\b(?!(?:18|19|20)\\d{2}\\b(?!\\.\\d))\\d*\\.?\\d+\\b"," ", "I'd like to delete numbers like 84 and 0.5 but not dates like 2015", perl=T). — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jan 5, 2016 at 11:29
@stribizhev this is perfect thanks. if you make it an answer I'll accept it and close the thread — Antoine
– Antoine, Commented Jan 5, 2016 at 11:32

Wiktor Stribiżew · Accepted Answer · 2016-01-05 11:37:48Z

2

As I mentioned in my comments, the main points here are:

regex pattern should be placed outside the character class to be treated as a sequence of subpatterns and not as separate symbols inside the class
the backslashes must be doubled in R regex patterns (since it uses C strings where \ is used to escape entities like \n, \r, etc)
and also you need to use perl=T with patterns featuring lookarounds (you are using lookaheads in yours)

Use

gsub("\\b(?!(?:18|19|20)\\d{2}\\b(?!\\.\\d))\\d*\\.?\\d+\\b"," ", "I'd like to delete numbers like 84 and 0.5 but not dates like 2015", perl=T)

answered Jan 5, 2016 at 11:37

Wiktor Stribiżew

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Comments

Andie2302 · Accepted Answer · 2016-01-05 11:27:16Z

1

To search and replace in R you can use:

gsub("\\b(?!(?:18|19|20)\\p{Nd}{2}\\b(?!\\.\\p{Nd}))\\p{Nd}*\\.?", "replacement_text_here", subject, perl=TRUE);

answered Jan 5, 2016 at 11:27

Andie2302

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