Add first element to a cell array
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Dear,
I would like to add a new element in the first position in an cell array For example if ArrCell={[1],[2],[3],[4],[5]} is the existing cell and [new] is a matrix. I would like to get ArrCell={[new],[1],[2],[3],[4],[5]}
Of course, I can get this result using a temporal cell array and looping over all the elements of the existing one, but the quesion is if there an efficient way to get this result
Thanks in advance,
采纳的回答
Adam
2015-12-18
ArrCell = [ { new }, ArrCell ];
should work. I'm not at my machine with Matlab at the moment so can't double-check, but fairly sure that works.
5 个评论
Luis Isaac
2015-12-18
Guillaume
2015-12-18
Note that there is no data structure matlab that allows for efficient insertion at the head of a container (as you're doing here). So, while the above way is efficient in that you don't have to write much code, it's still inefficient in that matlab has to reallocate a whole new array and copy all the data in the background. So your insertion is O(n).
Of course, it does not matter if your cell array is small enough.
Daniel van de Velden
2020-3-20
Correct answer would be:
ArrCell = [ { new }; ArrCell ];
Adam
2020-3-20
ArrCell was a row array. You can't concatenate vertically a scalar and a 5-element row array.
Image Analyst
2020-3-20
new = magic(3) % A matrix
ArrCell={[1],[2],[3],[4],[5]} % A cell array
ArrCell = [ { new }, ArrCell ] % Adam uses comma
ArrCell2 = [ { new }; ArrCell ]; % Daniel uses semicolon
new =
8 1 6
3 5 7
4 9 2
ArrCell =
1×5 cell array
{[1]} {[2]} {[3]} {[4]} {[5]}
ArrCell =
1×6 cell array
{3×3 double} {[1]} {[2]} {[3]} {[4]} {[5]}
Error using vertcat
Dimensions of arrays being concatenated are not consistent.
Error in test1 (line 12)
ArrCell2 = [ { new }; ArrCell ];
更多回答（3 个）
Image Analyst
2015-12-18
But the big question is why are you even using a cell array for that instead of a simple numerical array. Cell arrays are complicated and use a huge amount of overhead. From what you've shown there is no reason to use one. I recommend this instead
Arr = [1,2,3,4,5];
Arr = [new, 1,2,3,4,5]
2 个评论
Luis Isaac
2015-12-18
Josh
2024-5-4
appreciate this nudge in a more efficient direction, i fallback on cells arrays out of habit and ease but switching over to numerical arrays where possible...i make animations and cells help when image sizes are changing at least but seem uneccessary when image size is fixed
Fletcher Garrison
2021-2-3
编辑：Fletcher Garrison
2021-2-3
You can also use:
Arrcell = {1,2,3,4,5};
new = magic(5);
Arrcell = horzcat(new,Arrcell);
For future people looking this up:
testCell = {"one", 2, 10, "llama"}
testCell = {"newInput", testCell{:}}
1 个评论
I stand corrected by MATLAB autofix. Apparently this is faster.
testCell ={"one", 2, 10, "llama"}
testCell = [{"newInput"}, testCell(:).']
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