Concatenation of the strings vector in Clojure

Question

I would like to concatenate strings stored in a vector. For example if I have ["a" "b" "c"] in the vector I would like to get as a result "abc".

Solution 1

You can use clojure.string join function for that

(clojure.string/join ["a" "b" "c"])

Solution 2

You can use apply with the str function:

(apply str ["a" "b" "c"])

Solution 3

This is one of the ways Clojure's reduce can be used. Note the session at Clojure's REPL:

[dsm@localhost:~]$ clj
Clojure 1.4.0
user=> (reduce str ["a" "b" "c"])
"abc"
user=> 

Comments

[Adam Sznajder]

Is there any way to do this using map?

[Sergey]

You can use reduce here: (reduce str ["a" "b" "c"]) but I'd better use join function.

[NielsK]

If you don't need the separator of clojure.string/join, apply str is the better solution.

[Andrew Whitehouse]

(apply str <sequence>) is the approach you will see used most often (as NielsK says, as long as you don't need the separator)

[M Smith]

If you do want delimited you can use interpose thusly (apply str (interpose "," ["a" "b" "c"])) => "a,b,c"

[sheldonh]

@NielsK Why is str a better solution when no separator is required? I arrived here looking for the answer to that question. :-)

[NielsK]

1 - str is in core, so no need for extra namespaces to be loaded. 2 - In join without seperator there's a superfluous call for (.append sb "") per item in coll, which isn't done in str.

[NielsK]

If you only want to use delimiters for use in the final string, better use clojure.string/join, instead of apply str combined with interpose. The latter uses a lot more allocations. If you want to alter the collection some more before turning it into a string, interpose is the way to go though.

[NielsK]

While this may seem trivial, there's large performance gains to be had. Instead of calling str left and right during construction of very large strings, building a large collection and calling (apply str coll) (or even (apply str (flatten coll))) only once makes a huge difference.