Partial string matching using patterns

Question

I need to write a query in R to match partial string in column names. I am looking for something similar to LIKE operator in SQL. For e.g, if I know beginning, middle or end part of the string I would write the query in format:

LIKE 'beginning%middle%'

in SQL and it would return matching strings. In pmatch or grep it seems I can only specify 'beginning' , 'end' and not the order. Is there any similar function in R that I am looking for?

For example, say I am looking in the vector:

y <- c("I am looking for a dog",
       "looking for a new dog", "a dog", "I am just looking")

Let's say I want to write a query which picks "looking for a new dog" and I know start of the string is "looking" and end of string is "dog". If I do a grep("dog",y) it will return 1,2,3. Is there any way I can specify beginning and end in grep?

For example lets say I want to look into the vector y<- c("I am looking for a dog", "looking for a new dog", "a dog", "I am just looking"). Lets say I want to write a query which picks "looking for a new dog" and I know start of the string is "looking" and end of string is "dog". If I do a grep("dog",y) it will return 1,2,3,4. Is there any way I can specify beginning and end in grep? Thanks — DonDyck
– DonDyck, Commented May 28, 2014 at 1:46
I would edit your original question to include that example. That is important information. — MrFlick
– MrFlick, Commented May 28, 2014 at 1:51

MrFlick · Accepted Answer · 2014-05-28 01:53:56Z

7

The grep function supports regular expressions and with regular expressions, you can match almost anything

y<- c("I am looking for a dog", "looking for a new dog", "a dog", "I am just looking")
grep("looking.*dog",y, value=T)
# [1] "I am looking for a dog" "looking for a new dog"

Here this pattern looks for looking then "maybe something" then dog. So that should do what you want.

answered May 28, 2014 at 1:53

MrFlick

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James King · Accepted Answer · 2014-05-28 01:52:30Z

4

In regular expressions, ^ specifies the beginning of the string, $ specifies the end, thus:

y<- c("I am looking for a dog", "looking for a new dog", "a dog", "I am just looking")
grep("^looking.*dog$", y)
[1] 2

answered May 28, 2014 at 1:52

James King

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