Matching multiple patterns

Question

I want to see, if "001" or "100" or "000" occurs in a string of 4 characters of 0 and 1. For example, a 4 character string could be like "1100" or "0010" or "1001" or "1111". How do I match many strings in a string with a single command?

I know grep could be used for pattern matching, but using grep, I can check only one string at a time. I want to know if multiple strings can be used with some other command or with grep itself.

Answer 1

Yes, you can. The | in a grep pattern has the same meaning as or. So you can test for your pattern by using "001|100|000" as your pattern. At the same time, grep is vectorised, so all of this can be done in one step:

x <- c("1100", "0010", "1001", "1111") pattern <- "001|100|000"  grep(pattern, x) [1] 1 2 3 

This returns an index of which of your vectors contained the matching pattern (in this case the first three.)

Sometimes it is more convenient to have a logical vector that tells you which of the elements in your vector were matched. Then you can use grepl:

grepl(pattern, x) [1]  TRUE  TRUE  TRUE FALSE 

See ?regex for help about regular expressions in R.

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Edit: To avoid creating pattern manually we can use paste:

myValues <- c("001", "100", "000") pattern <- paste(myValues, collapse = "|") 

Answer 2

Here is one solution using stringr package

require(stringr) mylist = c("1100", "0010", "1001", "1111") str_locate(mylist, "000|001|100")