For loop to carry value down depending on another matrix value

Hello!

I have the following issue. I have 2 matrices (MatrixA and MatrixB), I want to create a third one(MatrixC) that uses the information on both as follows:

MatrixA MatrixB MatrixC

_______ _______ ______

0 150 0

0 1100 0

0 50 0

-1 20 0 When MatrixA switches from 0 to -1 use MatrixB Value,

-1 120 20 and copy that value all the way down until MatrixA

-1 70 20 turn to 1 and then repeat for every other instance

-1 90 20 very likely a for loop way.

1 100 20

0 101 0

-1 115 0

-1 110 115

-1 160 115

-1 200 115

-1 275 115

-1 400 115

-1 500 115

1 504 115

Preferably MatrixC maintains same size as MatixA OR MatrixC that’s why the zeros filling the gaps when it’s not applicable. Thanks so much for the help!

Answer 1

[J. Alex Lee]

In your example, there is a "delay" by 1 row when your switch from 0 to -1 occurs, so the following answer is not exactly producing the example, but maybe it can get you started

data = array2table([       0        150
       0       1100
       0         50
      -1         20
      -1        120
      -1         70
      -1         90
       1        100
       0        101
      -1        115
      -1        110
      -1        160
      -1        200
      -1        275
      -1        400
      -1        500
       1        504],"VariableNames",["A","B"])

data = 17×2 table
    A      B  
    __    ____

     0     150
     0    1100
     0      50
    -1      20
    -1     120
    -1      70
    -1      90
     1     100
     0     101
    -1     115
    -1     110
    -1     160
    -1     200
    -1     275
    -1     400
    -1     500

   data.C = nan(height(data),1);
   
% find where A switches from -1 to 0
sw = [false;diff(data.A)==-1]

sw = 17×1 logical array
   0
   0
   0
   1
   0
   0
   0
   0
   1
   1

% copy B into C when switch condition is met
data.C(sw) = data.B(sw)

data = 17×3 table
    A      B       C 
    __    ____    ___

     0     150    NaN
     0    1100    NaN
     0      50    NaN
    -1      20     20
    -1     120    NaN
    -1      70    NaN
    -1      90    NaN
     1     100    NaN
     0     101    101
    -1     115    115
    -1     110    NaN
    -1     160    NaN
    -1     200    NaN
    -1     275    NaN
    -1     400    NaN
    -1     500    NaN

% fix C to 0 when A=0
data.C(data.A==0) = 0

data = 17×3 table
    A      B       C 
    __    ____    ___

     0     150      0
     0    1100      0
     0      50      0
    -1      20     20
    -1     120    NaN
    -1      70    NaN
    -1      90    NaN
     1     100    NaN
     0     101      0
    -1     115    115
    -1     110    NaN
    -1     160    NaN
    -1     200    NaN
    -1     275    NaN
    -1     400    NaN
    -1     500    NaN

% fillmissing with previous value
data.C = fillmissing(data.C,"previous")

data = 17×3 table
    A      B       C 
    __    ____    ___

     0     150      0
     0    1100      0
     0      50      0
    -1      20     20
    -1     120     20
    -1      70     20
    -1      90     20
     1     100     20
     0     101      0
    -1     115    115
    -1     110    115
    -1     160    115
    -1     200    115
    -1     275    115
    -1     400    115
    -1     500    115

[IDN]

Thanks!