# How to replace specific values with 0's

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Hylke Dijkstra 2022 年 1 月 12 日
コメント済み: Hylke Dijkstra 2022 年 1 月 16 日
Dear all,
I have a 1435x205 matrix and I want to obtain the sum of a specific set of cells. In this case it is from the 146th to the 150th column and from the 316th to 351th row, which gives me a 35x5.
My first thought was to replace all values in the matrix except the specific values I just pointed out with 0's and then use a summation vector. Does anyone have an idea on how to do this? Preferably a generalized method.
For example assume that I have a 5x5 matrix
A = magic(5)
A =
17 24 1 8 15
23 5 7 14 16
4 6 13 20 22
10 12 19 21 3
11 18 25 2 9
And let's assume I want the values in the 2nd and 3rd row and the second and third row to be replaced by 0. Which gives me this result:
A =
0 0 0 0 0
0 5 7 0 0
0 6 13 0 0
0 0 0 0 0
0 0 0 0 0
Is there a simple command for this?
Finally, I want to sum these values (the total is 31):
sum=ones(1,5)*A*ones(5,1)
sum =
31
If anyone knows, is there a more succinct way to pick out which elements from a matrix matlabs sums using summation vectors?
Best wishes.
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Hylke Dijkstra 2022 年 1 月 16 日
Thanks!

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### 採用された回答

Voss 2022 年 1 月 12 日
A = rand(1435,205);
B = A(316:351,146:150) % 36-by-5
B = 36×5
0.0163 0.4406 0.9334 0.1858 0.1728 0.8915 0.0598 0.1625 0.4066 0.4813 0.2911 0.1403 0.6256 0.1844 0.0240 0.0914 0.8053 0.6554 0.6968 0.0514 0.7454 0.1218 0.6555 0.2145 0.0959 0.8615 0.8129 0.0892 0.5833 0.9865 0.5319 0.3094 0.7677 0.6644 0.7049 0.0716 0.0799 0.3528 0.8356 0.4728 0.5115 0.1830 0.8823 0.2619 0.9479 0.6841 0.0168 0.4885 0.6340 0.3808
sum(B(:))
ans = 85.1768
or:
sum(sum(A(316:351,146:150)))
ans = 85.1768
or:
sum(A(316:351,146:150),'all')
ans = 85.1768

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### その他の回答 (1 件)

Hylke Dijkstra 2022 年 1 月 16 日
Thanks!

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R2021a

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