CODEWITHSUNDEEP
r
Vinterwoo
Vinterwoo

Reputation: 3941

Does R have a wildcard expression (such as an asterisk (*))?

I hope I am not missing something obvious but here is my question:

Given data like this

Data1=
Name       Number
AndyBullxxx    12
AlexPullxcx    14
AndyPamxvb     56
RickRalldfg    34
AndyPantert    45
SamSaltedf     45

I would like to be able to pull out all of the rows starting with "Andy"

subset(Data1,Name=="Andy*")

AndyBullxxx  12
AndyPamxvb   56
AndyPantert  45

So basically a wild card symbol that will let me subset all rows that begin with a certain character designation.

Upvotes: 17

Views: 96683

Answers (3)

Ramnath
Ramnath

Reputation: 55715

If you are not comfortable with regex there is a function in the utils package, which can convert wildcard based expressions to regex. So you can do

df[grepl(glob2rx('Andy*'), rownames(df)),]

Upvotes: 13

Matt Bannert
Matt Bannert

Reputation: 28274

Try, 

df[grep("^Andy",rownames(df)),]

the first argument of grep is a pattern, a regular expression. grep gives back the rows that contain the pattern given in this first argument. the ^ means beginning with.

Let's make this reproducible:

 df <- data.frame(x=c(12,14,56,34,45,45))
 rownames(df) <- c("AndyBullxxx", "AlexPullxcx","AndyPamxvb", "RickRalldfg","AndyPantert","SamSaltedf")
 ## see what grep does
 grep("^Andy",rownames(df))

Upvotes: 25

Paul Hiemstra
Paul Hiemstra

Reputation: 60964

I think you want to go for a regular expression:

subset(Data1, grepl("^\bAndy", Name))

or 

Data1[grepl("^\bAndy", Data1$Name),]

In the regular expression the "^" stands for startswith, and \b for the next set of characters is going to be a word. Regular expressions are a powerful text processing tool that require some study. There are a lot of tutorials and websites online. One of them that I use is:

http://www.regular-expressions.info/

I can't use R right now (my wifes laptop ;)), so these pieces of code go untested. Maybe next time provide us with an example dataset, that makes it really easy to provide a working example.

Upvotes: 3

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