清空筛选条件
清空筛选条件

size of nonzero entries in each row of a matrix without loop

22 次查看（过去 30 天）
Maider Marin
Maider Marin 2011-2-8
评论： Mbvalentin 2016-3-14
Let's explained with an example if I have h =
0 1 2 3
1 0 0 0
5 0 1 0
there is any function that will return the number of nonzero elements per row something like c =
3
1
2
but without a loop. I know I can use nnz per row
something like
for i=1: numRows
c(i)=nnz(h(i,:));
end
but there is any way to do it without a loop?
I will really appreciate any suggestions

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2011-2-8
c = sum(h~=0,2);
  6 个评论
显示 4更早的评论
Maider Marin
Maider Marin 2011-2-14
yes, it is true...my familiarity with the command did not let me, understand it. Thans a buch Walter and Matt
Paulo Silva
Paulo Silva 2011-3-15
B = sum(A,dim) sums along the dimension of A specified by scalar dim. The dim input is an integer value from 1 to N, where N is the number of dimensions in A. Set dim to 1 to compute the sum of each column, 2 to sum rows, etc.

请先登录，再进行评论。

更多回答（3 个）

stef stef
stef stef 2011-3-15
thank you Walter!Your answer worked fine with me, although i didn't exactly understand what 0,2 does..I thought sum was only to add values of elements.
  1 个评论
Mbvalentin
Mbvalentin 2016-3-14
It's not a decimal point (like a = 0,2). The comma is just dividing the two input arguments that the 'sum' function can take. In this case he is first creating a logical matrix that has ones for every element in h that is not equal to 0 (that's what h ~= 0 does), and then this result vector is inputed in the sum function.
Now, the sum function does the summatory of the input vector (or matrix) in a certain direction. The default direction is '1' (this is, along the row direction). I.E., assume we have the following matrix:
M = [10 10 0; 0 10 1; 1 0 1];
The result of L = (M ~= 0) would be:
L = [1 1 0; 0 1 1; 1 0 1];
Now, the results of the sum of 'M' on each direction are:
sum(M,1) = [11, 20 2]; sum(M,2) = [20; 11; 2].
As the result of the logical matrix L is a one row vector, we need to add the values along the 'columns-direction', which is '2'. That's why here Walter used the sum(MATRIX,2), to sum along the columns.

请先登录，再进行评论。

Paulo Silva
Paulo Silva 2011-3-15
Another option but not so good like Walter suggestion
a=[0 1 2 3
1 0 0 0
5 0 1 0]
sum(arrayfun(@any,a(1:size(a,1),:)),2)
ans =[3;1;2]
Gabriel
Gabriel 2013-7-2
Keep in mind, the previous answers may work, but they require a lot of memory if your array is big (basically duplicates it).
If working with a LOT of data and facing out of memory errors, the for loop with nnz might be the way to go.

类别

在 Help Center 和 File Exchange 中查找有关 Loops and Conditional Statements 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by