How to delete zero components in a vector in Matlab

Question

I have a vector for example  a    0 1 0 3    I want to turn a into b which equals b    1 3    How do I perform this in general  So I have a vector with some zero components and I want to remove the zeroes and leave just the non-zero numbers

User · Answer

I just came across this problem and wanted to find something about the performance, but I couldn't, so I wrote a benchmarking script on my own:

% Config:
rows = 1e6;
runs = 50;

% Start:
orig = round(rand(rows, 1));

t1 = 0;
for i = 1:runs
    A = orig;
    tic
    A(A == 0) = [];
    t1 = t1 + toc;
end
t1 = t1 / runs;

t2 = 0;
for i = 1:runs
    A = orig;
    tic
    A = A(A ~= 0);
    t2 = t2 + toc;
end
t2 = t2 / runs;

t1
t2
t1 / t2

So you see, the solution using A = A(A ~= 0) is the quicker of the two :)

User · Answer

I often ended up doing things like this  Therefore I tried to write a simple function that  snips  out the unwanted elements in an easy way  This turns matlab logic a bit upside down  but looks good   b   snip a  0     you can find the function file at  http   www mathworks co uk matlabcentral fileexchange 41941-snip-m-snip-elements-out-of-vectorsmatrices  It also works with all other  x   nan or whatever elements

User · Answer

You could use sparse a   which would return   1 2         1   1 4         3  This allows you to keep the information about where your non-zero entries used to be

User · Answer

Data  a  0  3   0   0   7   10   3   0   1   0   7   7   1   7   4    Do  aa nonzeros a     Result  aa  3   7   10   3   1   7   7   1   7   4

User · Answer

If you just wish to remove the zeros  leaving the non-zeros behind in a  then the very best solution is  a a  0          This deletes the zero elements  using a logical indexing approach in MATLAB  When the index to a vector is a boolean vector of the same length as the vector  then MATLAB can use that boolean result to index it with  So this is equivalent to  a find a  0           And  when you set some array elements to    in MATLAB  the convention is to delete them   If you want to put the zeros into a new result b  while leaving a unchanged  the best way is probably  b   a a    0     Again  logical indexing is used here  You could have used the equivalent version  in terms of the result  of  b   a find a    0      but mlint will end up flagging the line as one where the purely logical index was more efficient  and thus more appropriate   As always  beware EXACT tests for zero or for any number  if you would have accepted elements of a that were within some epsilonic tolerance of zero  Do those tests like this  b   a abs a   gt   tol     This retains only those elements of a that are at least as large as your tolerance

User · Answer

b   a find a  0

User · Answer

Why not just  a a   a  or a  a       It s equivalent to the other approaches but certainly less key strokes

[matlab] How to delete zero components in a vector in Matlab?

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