The split in both clojure and java takes regular expression as parameter to split. But I just want to use normal char to split. The char passed in could be "|", ","," " etc. how to split a line by that char?
I need some function like (split string a-char). And this function will be called at very high frequency, so need good performance. Any good solution.
There are a few features in java.util.regex.Pattern class that support treating strings as literal regular expressions. This is useful for cases such as these. @cgrand already alluded to (Pattern/quote s) in a comment to another answer. One more such feature is the LITERAL flag (documented here). It can be used when compiling literal regular expression patterns. Remember that #"foo" in Clojure is essentially syntax sugar for (Pattern/compile "foo"). Putting it all together we have:
(import 'java.util.regex.Pattern)
(clojure.string/split "foo[]bar" (Pattern/compile "[]" Pattern/LITERAL))
;; ["foo" "bar"]
Just make your character a regex by properly escaping special characters and use the default regex split (which is fastest by far).
This version will make a regexp that automatically escapes every character or string within it
(defn char-to-regex
[c]
(re-pattern (java.util.regex.Pattern/quote (str c))))
This version will make a regexp that escapes a single character if it's within the special character range of regexps
(defn char-to-regex
[c]
(if ((set "<([{\\^-=$!|]})?*+.>") c)
(re-pattern (str "\\" c))
(re-pattern c)))
Make sure to bind the regex, so you don't call char-to-regex over and over again if you need to do multiple splits
(let [break (char-to-regex \|)]
(clojure.string/split "This is | the string | to | split" break))
=> ["This is " " the string " " to " " split"]
