Mathematica: adding a list of lists elementwise

Question

I have a list of lists of numbers. I add them into one list by adding all of the first elements together, all of the second elements together, etc. For example, if my list were { {1,2,3}, {1,2,3}, {1,2,3,4} } I would want to end up with {3,6,9,4}. How do I do this in Mathematica?

score 2 · Answer 1 · answered Aug 01 '15 at 11:16

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a = {{1, 2, 3}, {1, 2, 3}, {1, 2, 3, 4}};

Total@PadRight@a

{3, 6, 9, 4}

answered Aug 01 '15 at 11:16

Chris Degnen

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score 1 · Answer 2 · edited Apr 13 '17 at 12:55

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Among its many useful features, Flatten will transpose a 'ragged' array (see here for a nice explanation, or check out the 'applications' subsection of the documentation on Flatten)

Total /@ Flatten[#, {{2}}] &@{{1, 2, 3}, {1, 2, 3}, {1, 2, 3, 4}}

{3, 6, 9, 4}

edited Apr 13 '17 at 12:55

Community

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answered Mar 08 '16 at 10:29

681234

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score 0 · Answer 3 · answered Aug 01 '15 at 03:49

If all the rows were the same length then adding the rows would do this.

So make all the rows the same length by appending zeros and then add them.

lists = {{1, 2, 3}, {1, 2, 3}, {1, 2, 3, 4}};
max = Max[Length /@ lists]; min = Min[Length /@ lists];
zeros = Table[0, {max - min}];
Plus @@ Map[Take[Join[#, zeros], max] &, lists]

Mathematica: adding a list of lists elementwise

3 Answers3