Cant find the number of row for big size of matrix

Question

fyza affandi 2019-1-4

0
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https://ww2.mathworks.cn/matlabcentral/answers/438202-cant-find-the-number-of-row-for-big-size-of-matrix

评论： madhan ravi 2019-1-4

I have a tblBarray matrix of size 13x1

and from given list of E3,

    Columns 1 through 18
     1     1     4     5     1     1     3     1     1     1     2     5     1     1     1     1     3     4
  Columns 19 through 36
     1     3     5    10     5     4     4     2     3     4     5     8     4     1     1     2    12    16
  Columns 37 through 54
     1     1     3     3     1     2    10    14     1     1     1     1     1     1    10     8     2     5
  Columns 55 through 64
     3    15     5     2     1     3     2    21     1    11

I need to search which row thet are belong to that tblBarray

I use this code below

for nE3=1:length (E3)
   e31= find(E3(nE3)==tblBarray);
   e3=[e3,e31]; 
end

And get the answer

   1     1     5     4     1     1     2     1     1     1     3     4     1     1     1     1     2
  Columns 18 through 34
     5     1     2     4     6     4     5     5     3     2     5     4     7     5     1     1     3
  Columns 35 through 51
     9    12     1     1     2     2     1     3     6    10     1     1     1     1     1     1     6
  Columns 52 through 64
     7     3     4     2    11     4     3     1     2  

Then I try for a bigger size of tblBarray unfortunately, it takes a very long time. Can anyone help me how can I solve this? Do i need to change 'find' function? If so, how can I change it?

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Answer 1

per isakson 2019-1-4

2
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https://ww2.mathworks.cn/matlabcentral/answers/438202-cant-find-the-number-of-row-for-big-size-of-matrix#answer_354918

编辑：per isakson 2019-1-4

在 MATLAB Online 中打开

The editor warns you that there is an issue with your code.

Notice the orange signs in the column to the right of the editor text pane.
The variable e3 is underlined

Right click the underlined e3

If you have not already preallocated e3, you shall do that.

See Techniques to Improve Performance

Compare the speed of your loop with this one

%%
e3 = nan( size(E3) ); 
for nE3=1:length (E3)
   e3(nE3) = find(E3(nE3)==tblBarray);
end

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per isakson 2019-1-4

Matlab for-loops have a reputation for being slow. However, nowadays they are much faster than they used to be. In your case, I guess the problem is find, especially if tblBarray is large.

Compare the speed with the solution of madhan ravi . I guess that one is faster.