find function on specific row and column of an array.

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JohnDylon
JohnDylon 2016-10-29
编辑： Image Analyst 2016-10-30
Hi,
I used find function in order to find row location of an array cell. To illustrate in an example:
A=magic(10)
A =
92 99 1 8 15 67 74 51 58 40
98 80 7 14 16 73 55 57 64 41
4 81 88 20 22 54 56 63 70 47
85 87 19 21 3 60 62 69 71 28
86 93 25 2 9 61 68 75 52 34
17 24 76 83 90 42 49 26 33 65
23 5 82 89 91 48 30 32 39 66
79 6 13 95 97 29 31 38 45 72
10 12 94 96 78 35 37 44 46 53
11 18 100 77 84 36 43 50 27 59
find(A(4:5,4)==21)
ans =
1
What I wanted to get is in intersection of a row window and a specific column, I wanted to find a specific input's row location in the matrix. I expected to find the row number as 4, however I get 1. Find function thinks A(4:5,4) is a new array and gives locations accordingly.
Does anyone know how to get the true row location when I specify an mxn sub-matrix in a rxs matrix where r>m, s>n?
Thx,
JD

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采纳的回答

Image Analyst
Image Analyst 2016-10-30
编辑：Image Analyst 2016-10-30
To find a submatrix in another matrix, use ismember:
m = magic(10)
subm = m(4:6, 3:8)
% c = normxcorr2(subm, m)
[ia, ib] = ismember(m, subm)

更多回答（1 个）

Image Analyst
Image Analyst 2016-10-29
Just don't specify a sub-matrix. Why are you doing that? It just ruins it and doesn't give you what you want. Just do it like this:
A=magic(10)
[rows, columns] = find(A == 21)
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JohnDylon
JohnDylon 2016-10-29
编辑：JohnDylon 2016-10-29
Before code finds its location, I don't know it is at (9,4) coordinate in the array. I expect the code finds it, I just told it in order to make my problem clear.
Matrix A is like
A=
1 24 1 1 15
2 5 1 2 16
3 6 1 3 22
4 12 1 4 3
5 18 1 5 9
6 13 2 1 1
7 20 2 2 13
8 5 2 2 8
9 14 2 3 19
10 6 2 4 1
11 28 3 1 22
12 25 3 2 23
13 20 3 3 21
14 21 3 4 26
15 27 3 5 27
It has a sub matrix
A1=
6 13 2 1 1
7 20 2 2 13
8 5 2 2 8
9 14 2 3 19
10 6 2 4 1
and I wanted to find row location of A(7,4) however I didn't know it was at the 7th row at first place, I needed that info.
I guess find still can work for this specific problem with
row=find(A(:,3)==2 & A(:,4)==2, 1, 'first')
that generates row=7 and
row=find(A(:,3)==2 & A(:,4)==2, 1, 'last')
that generates row=8.
Thank you for help.
JD
Image Analyst
Image Analyst 2016-10-29
So you want to do basically a template matching. You have a known submatrix and want to find its location inside a larger matrix. You can use normxcorr2() to do that. I attach a demo.

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