String manipulations in R (May 10, 2005). Category: Data management, Category: R software
As part of my efforts to analyze microarray data, I am finding that I need to do simple string manipulations in R. Here is a list of functions that might help.
- paste() combines several strings together into a single string.
- substr() selects substrings.
- format() makes a set of numbers print out more nicely.
There are several functions that will convert one string into another string.
- chartr() converts specific characters in a string to different characters.
- tolower() converts all the letters in a string to lower case.
- toupper() converts all the letters in a string to upper case.
- casefold() will perform either of the two conversions shown above.
Several functions help find matches between two lists.
- a %in% b returns a logical value of TRUE for each value of a which can be found somewhere in list b and FALSE if that value cannot be found.
- pmatch(), match(), charmatch() work similarly but with subtle variations.
Several functions will use regular expressions.
- grep() searches for matches to a pattern.
- strsplit() splits a string into several pieces.
A nice tutorial, by the way, on regular expressions is at:
There are several string manipulation functions found in the limma package, including
- makeUnique() is found in the limma package and adds numbers to the ends of duplicate strings to give each one a unique name.
- trimWhiteSpace() is found in the limma package and removes leading and trailing blanks from a string.
This webpage was written by Steve Simon and was last modified on 07/08/2008.