Adding random data to left and right of each element in a matrix

Question

Joseph Lee 2017-11-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/367403-adding-random-data-to-left-and-right-of-each-element-in-a-matrix

评论： Joseph Lee 2017-11-20

采纳的回答： Stephen23

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This is a change from my previous question with random elements instead of fixed elements

https://www.mathworks.com/matlabcentral/answers/365828-adding-data-to-two-matrices-for-indexing#answer_290019

Take for example,

i have two 3x4 matrices, M=

     2        3          4
     6        7          8
    10        11        12

and E which shows the number of elements to be added to matrix M, random from 1-4

     2        1          2
     3        4          1
     3        2          3

The elements to be added are random numbers from 0.1 to 0.9, the result to be obtained is shown below

3   1.9   1.4   1.1   1  1.5   1.3   1.9   1.7        2.2    2.4   2   2.9   2.5      3.1  3  3.7     4.8   4.2   4   4.4   4.1
3   5.8   5   5.5   5.1        6.6   6.1   6.3   6   6.2   6.2   6.7       7.2   7.3   7.2   7.9   7   7.1   7.5   7.4        8.8   8   8.2 
2   9   9.5   10.9   10.7   10.6   10   10.4   10.3   10.4   11.3   11.4   11   11.1   11.9       12.3   12.9   12.5   12   12.3   12.4   12.8

Next is how do i store this data since it no longer stays as a matrix and is it possible use indexing to find a certain value eg. find(M==2)

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Andrei Bobrov 2017-11-16

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how?

>> sum([4       2        1          2
    2       3        4          1
    1       3        2          3],2)
ans =
     9
    10
     9
>>

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Answer 1

Stephen23 2017-11-16

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/367403-adding-random-data-to-left-and-right-of-each-element-in-a-matrix#answer_291508

编辑：Stephen23 2017-11-16

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M = [
  1       2        3          4
  5       6        7          8
  9      10        11        12];
E = [
    4       2        1          2
    2       3        4          1
    1       3        2          3];
%
foo = @(m,e) m+randi(9,1,e)/10;
fun = @(m,e) [foo(m,e),m,foo(m,e)];
C = arrayfun(fun,M,E,'Uni',0);

Giving the output in a cell array C, where each cell contains a vector based on one element of M, e.g. the first column of C:

>> C{:,1}
ans =
   1.4000   1.3000   1.9000   1.3000   1.0000   1.9000   1.1000   1.3000   1.9000
ans =
   5.6000   5.6000   5.0000   5.9000   5.5000
ans =
   9.1000   9.0000   9.3000
>>

" how do i store this data since it no longer stays as a matrix..."

I showed you how to put this into a cell array which is the same size as your original matrices. Alternatively you could extract all of the numeric data and concatenate it into one long numeric vector.

"...and is it possible use indexing to find a certain value eg. find(M==2)"

That depends on how your decide to store it: storing in a cell array requires a different way of searching than if you use one numeric vector.

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Stephen23 2017-11-16

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Use a cell array, add it as an input to cellfun. something like this::

H = {[0.2 0.8 0.3 0.5],[10,20],...}
M = [...];
fun = @(m,h) [fliplr(h)+m,m,m+h];
cellfun(fun,num2cell(M),H,'Uni',0)

Joseph Lee 2017-11-20

Thanks! It works. Now to the indexing part,I will be posting a new question for this.

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Answer 2

Image Analyst 2017-11-16

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https://ww2.mathworks.cn/matlabcentral/answers/367403-adding-random-data-to-left-and-right-of-each-element-in-a-matrix#answer_291507

Since the padding on either side of each element of M is determined by the value of the corresponding element of E, and the sum of the rows in E do not sum to a constant, the rows in the final result will probably not all be the same length. Thus you will need to use a cell array.

It will be very easy for you to do this yourself once you're read the FAQ on cell arrays: http://matlab.wikia.com/wiki/FAQ#What_is_a_cell_array.3F