Return Matrix to Original Order

Question

Konstantinos Tsitsilonis 2017-8-2

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https://ww2.mathworks.cn/matlabcentral/answers/351339-return-matrix-to-original-order

评论： Konstantinos Tsitsilonis 2017-8-3

Hi all,

I have a column vector RPM_c, where I want to split it to elements below and above the vector's mean value, perform a different operation in the two respective groups of elements, and place them back to their original position as found RPM_c.

I know how to do everything, except for the last part of placing them in their original position. For example:

 RPM_c = [m x 1] ; %an m x 1 matrix
 %Find elements above and below the mean
 RPM_L = RPM_c(RPM_c < mean(RPM_c)) ;
 RPM_H = RPM_c(RPM_c > mean(RPM_c)) ; 
 %Perform any desired operation on these elements 
 %(it could be anything, for this example I choose to smooth & multiply the two groups respectively)
 RPM_Ls = smooth(RPM_L, 'rlowess') ; 
 RPM_Hs = RPM_H * 1.16 ;

Now I need to place RPM_Ls and RPM_Hs back in their original order, as found in vector RPM_c. How could I do this? I am trying to avoid sorting the data. I know this would be easier, however it is of importance in this case that they remain with their current order.

Thanks for your help in advance,

KMT.

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Answer 1

James Tursa 2017-8-2

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https://ww2.mathworks.cn/matlabcentral/answers/351339-return-matrix-to-original-order#answer_276556

编辑：James Tursa 2017-8-2

在 MATLAB Online 中打开

Keep track of the original indexing. E.g.,

>> RPM_c = randperm(15)  % sample data
RPM_c =
    10     9    15     6    13     2     1    11    14     3     8     7     4     5    12
>> x = RPM_c < mean(RPM_c)  % logical indexes of the Lower stuff
x =
     0     0     0     1     0     1     1     0     0     1     0     1     1     1     0
>> RPM_L = RPM_c(x)  % get the Lower stuff
RPM_L =
     6     2     1     3     7     4     5
>> RPM_H = RPM_c(~x)  % get the Upper stuff
RPM_H =
    10     9    15    13    11    14     8    12
>> RPM_L = RPM_L * 2  % do something to the Lower stuff
RPM_L =
    12     4     2     6    14     8    10
>> RPM_H = RPM_H / 2  % do something to the Higher stuff
RPM_H =
    5.0000    4.5000    7.5000    6.5000    5.5000    7.0000    4.0000    6.0000
>> RPM_c(x) = RPM_L  % put the Lower stuff back into original spots
RPM_c =
    10     9    15    12    13     4     2    11    14     6     8    14     8    10    12
>> RPM_c(~x) = RPM_H  % put the Higher stuff back into original spots
RPM_c =
  Columns 1 through 11
    5.0000    4.5000    7.5000   12.0000    6.5000    4.0000    2.0000    5.5000    7.0000    6.0000    4.0000
  Columns 12 through 15
   14.0000    8.0000   10.0000    6.0000

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Answer 2

John BG 2017-8-2

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https://ww2.mathworks.cn/matlabcentral/answers/351339-return-matrix-to-original-order#answer_276555

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Hi Konstantinos

this is John BG <mailto:jgb2012@sky.com jgb2012@sky.com>

1.

Instead of

 RPM_L = RPM_c(RPM_c < mean(RPM_c))
 RPM_H = RPM_c(RPM_c > mean(RPM_c))

use command find, obtaining the positions of the found elements.

For instance, for the values below mean

RPM_c=randi([-10 10],m,1)
RPM_c =
     7
     9
    -8
     9
     3
    -8
    -5
     1
    10
    10
[Li,Lv]=find(RPM_c<mean(RPM_c))
Li =
     3
     6
     7
     8
Lv =
     1
     1
     1
     1

Lv not used.

Now in Li you have the positions of the elements with values below mean(RPM_c)

Same for values above mean:

[Ui,Uv]=find(RPM_c<mean(RPM_c))
Ui =
     3
     6
     7
     8
Uv =
     1
     1
     1
     1

2.

Obtaining the values to process

RPM_L=RPM_c(Li)
RPM_H=RPM_c(Ui)
RPM_L =
    -8
    -8
    -5
     1
RPM_H =
    -8
    -8
    -5
     1

3.

Processing

RPM_Ls = smooth(RPM_L, 'rlowess')  
RPM_Hs = RPM_H * 1.16  
RPM_Hs = RPM_H * 1.16  
RPM_Ls =
   -8.3274
   -7.1224
   -4.1224
    0.6726
RPM_Hs =
   -9.2800
   -9.2800
   -5.8000
    1.1600

4.

Compiling results

RPM_result=RPM_c;

if any value is exactly the mean value it remains in same position.

RPM_result(Li)=RPM_Ls
RPM_result(Ui)=RPM_Hs
RPM_result =
    7.0000
    9.0000
   -8.3274
    9.0000
    3.0000
   -7.1224
   -4.1224
    0.6726
   10.0000
   10.0000
RPM_result(Ui)=RPM_Hs
RPM_result =
    7.0000
    9.0000
   -9.2800
    9.0000
    3.0000
   -9.2800
   -5.8000
    1.1600
   10.0000
   10.0000