extracting row and column indices from MatLab matrix

Question

Laszlo Bodnar 2016-2-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/269732-extracting-row-and-column-indices-from-matlab-matrix

评论： Laszlo Bodnar 2016-2-25

I have a simple matrix that I have imported into MatLab using the following code:

 D_input=[0 1 2 1 ; nan 0 2 1 ; nan nan 0 1 ; nan nan 1 0];
 D_input

Now what I want to do is I would like to see the outputs in vector format, so I applied the following code:

reshape(D_input,1,numel(D_input))

It works perfectly fine:

0 NaN NaN NaN 1 0 NaN NaN 2 2 0 1 1 1 1 0

Now is there a way to display the row and column indices above this result, I mean something like this:

 (a – using row col indices)) (1,1) (2,1) (3,1) (4,1) (1,2) (2,2) (3,2) etc.
 (b – using linear indexing)    1     2     3     4     5     6     7 etc.
 (c – output)                   0    NA    NA    NA     1     0    NA etc.

I know about version b (linear indexing) but still I would prefer version a, displaying the row and column indices of D_input matrix as indicated. Is there an easy way to do this?

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Answer 1

Jos (10584) 2016-2-24

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https://ww2.mathworks.cn/matlabcentral/answers/269732-extracting-row-and-column-indices-from-matlab-matrix#answer_211013

在 MATLAB Online 中打开

You can transform linear indices into subindices, and vice versa using ind2sub and sub2ind

A = [99 NaN ; 8 7 ; 1 0]
LinearIndices = 1:numel(A)
[RowInd, ColInd] = ind2sub(size(A), 1:numel(A))

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Laszlo Bodnar 2016-2-25

Thank you Jos for the quick help!

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Answer 2

Stephen23 2016-2-24

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/269732-extracting-row-and-column-indices-from-matlab-matrix#answer_211012

编辑：Stephen23 2016-2-24

在 MATLAB Online 中打开

D_input = [0 1 2 1 ; nan 0 2 1 ; nan nan 0 1 ; nan nan 1 0]
S = size(D_input);
[X,Y] = ndgrid(1:S(1),1:S(2));
fprintf(' (%d,%d)',[X(:)';Y(:)'])
fprintf('\n')
fprintf('%5d ',1:prod(S))
fprintf('\n')
fprintf('%5d ',D_input)
fprintf('\n')

displays this in the command window:

 (1,1) (2,1) (3,1) (4,1) (1,2) (2,2) (3,2) (4,2) (1,3) (2,3) (3,3) (4,3) (1,4) (2,4) (3,4) (4,4)
    1     2     3     4     5     6     7     8     9    10    11    12    13    14    15    16
    0   NaN   NaN   NaN     1     0   NaN   NaN     2     2     0     1     1     1     1     0

Note: this solution works for integer values with fewer than five digits, and matrices with size less than 10 along any dimension. For larger numbers or matrices you will need to play around with the spacing and fieldwidth of the fprintf format tokens.

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Guillaume 2016-2-24

在 MATLAB Online 中打开

Note that you may want to use

fprintf('%5g ',D_input)

If the D_input can contain non-integer numbers

Laszlo Bodnar 2016-2-25

Thank you Stephen & Guillaume for your replies. Although I will use Jos's code in my exercise, I will also memorize your solution which is quite elegant and surely come in handy later on. Thanks again.

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