Merging two lists by prepending elements

Question

Being a newcomer to Mathematica, I have the following question.

Given

x = Range@9~Partition~3;

and

y = {a, b, c};

I want to combine x and y so that

result = {{a, 1, 2, 3}, {b, 4, 5, 6}, {c, 7, 8, 9}};

I have written

MapPrepend[a_, b_] := Prepend[a[[#]], b[[#]]] & /@ Range@Length@b

which does the job, but I wonder if there are other, more functional solutions?

Probably this question has already been answered. In this case it would be very nice if you just would direct me to the links.

Please take a look here, there is something for everyone: mathematica.stackexchange.com/questions/3069/… — Yves Klett, Commented May 14, 2014 at 18:59
@kguler - thanks, short and elegant (sometimes you don't see the wood for the trees). Should also be faster on large lists;) — eldo, Commented May 14, 2014 at 19:10

Yves Klett · Accepted Answer · 2014-05-14 19:02:10Z

2

I would simply do Flatten /@ Transpose[{y, x}].

Yves Klett

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answered May 14, 2014 at 19:00

Wouter

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$\begingroup$ also very nice, thank you. To not forget it I just added to my init.m a "MapFlatten". $\endgroup$
– eldo
Commented May 14, 2014 at 19:29

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Jacob Akkerboom · Accepted Answer · 2014-05-14 18:59:28Z

3

Unfortunately, in terms of speed there is probably not much to gain here. However, I guess this is fancy

Join[List /@ y, x, 2]

answered May 14, 2014 at 18:59

Jacob Akkerboom

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$\begingroup$ The shortest characterwise. Didn't know that "Join" accepts a level parameter. $\endgroup$
– eldo
Commented May 14, 2014 at 19:36
1

$\begingroup$ @eldo copy this: {y, ## & @@ x}\[Transpose] $\endgroup$
– Kuba
Commented May 14, 2014 at 21:01
1

$\begingroup$ @Kuba I can't beat that :). My shortest: {y, x /. _@z__ -> z}\[Transpose] $\endgroup$
– Jacob Akkerboom
Commented May 14, 2014 at 21:34
$\begingroup$ @JacobAkkerboom nice syntax :) it's interesting to see others habits :) $\endgroup$
– Kuba
Commented May 14, 2014 at 21:40

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2 Answers 2