1
$\begingroup$

How to join several list putting some fixed list between?

Like this

MyJoin[{{a,b},{c,d},{e,f}},{x}]

giving

{a, b, x, c, d, x, e, f}

This is like join with connector.

$\endgroup$
0

2 Answers 2

5
$\begingroup$

You can use Riffle and Join:

MyJoin[list_,glue_] := Join @@ Riffle[list, {glue}]

or as a pure function

MyJoin = Join @@ Riffle[#, {#2}] &
$\endgroup$
2
  • 2
    $\begingroup$ The exhibited function does not work for the example shown in the question. This is because Riffle interprets a list in the second argument as a cyclic replacement specification. The second argument must be wrapped in a list to work around this interpretation: MyJoin[list_,glue_] := Join @@ Riffle[list, {glue}] or MyJoin = Join @@ Riffle[#, {#2}] &. $\endgroup$
    – WReach
    Jan 4, 2015 at 22:22
  • $\begingroup$ @WReach Oh, good catch, thanks a lot! $\endgroup$ Jan 4, 2015 at 22:26
2
$\begingroup$

You can also use this:

MyJoin = Flatten@*Riffle;

MyJoin[{{a, b}, {c, d}, {e, f}}, {x}]
(*{a, b, x, c, d, x, e, f}*)

As Martin Büttner pointed out, this will flatten internal structures in nested lists, which may or may not be what you are looking for.

$\endgroup$
6
  • $\begingroup$ What is "@*"? Can't find it $\endgroup$
    – Suzan Cioc
    Jan 4, 2015 at 17:52
  • $\begingroup$ @SuzanCioc It's function composition. Note that using Flatten will not preserve any structure within your initial list (i.e. if either argument contains nested lists, those will be flattened as well). $\endgroup$ Jan 4, 2015 at 17:52
  • $\begingroup$ @MartinBüttner: It's actually new in Mathematica 2 :) $\endgroup$ Jan 4, 2015 at 17:53
  • $\begingroup$ @DumpsterDoofus Oh... then I only discovered it recently. (Ah, RightComposition aka /* is what's new in 10.) $\endgroup$ Jan 4, 2015 at 17:53
  • $\begingroup$ Apparently it existing but not shortened to "@*" in my Mathematica. $\endgroup$
    – Suzan Cioc
    Jan 4, 2015 at 18:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.