The way you use grep here will use the user-supplied string as a regular expression (a pattern, such as cat.dog), not necessarily as a plain fixed string. This will be an integer vector unless the input is a long vector, when it will be a double vector. Dont single-quote the variable (it will prevent the shell from expanding its value). First of all, note that this RegExp uses the 'Extended regular expression' syntax (ERE) - the + is a metacharacter that doesn't work in the 'Basic regular expression' syntax that grep uses by default (meaning it would match itself and require a literal + at that position), so if you want to use that RegEx with grep, you will need to pass the -E option. By default, devices are read if they are on the command line or if the -R. Ignored (with a warning) unless value TRUE. This is useful with options that prefix their output to the actual content: -H. If TRUE return indices or values for elements that do not match.

If TRUE all matches are returned, otherwise just the first one. If TRUE, pattern is a pattern to be matched as is. Grep2(value = FALSE) returns a vector of the indices of the elements of x that yielded a match (or not, for invert = TRUE). Determines the return value: see ‘Value’. If FALSE, a vector containing the (integer) indices of the matches determined by grep2 is returned, and if TRUE, a vector containing the matching elements themselves is returned. Usage grep2(pattern, x, value = TRUE, invert = FALSE, perl = FALSE)Ĭharacter vector containing regular expression as cells to be matched in the given character vector.Ī character vector where matches are sought, or an object which can be coerced by as.character to a character vector. Allows to identify and extract cells with/without multiple search patterns that are connected with AND.

R value true grep examples