Sorting Matrix where column specifies condition next element needs to meet

Hello,

Say I have a long table with elements and an array

% table with distinct elements for A1. A2 is sometimes an integer and
% sometimes -1000 
T   A1    A2 
0	182	181
1	182	180
2	181	180
3	45	-1000
4	29	-1000

% array specifies whether A2 should have -1000 
 [True False True False False] 

Separately, i have an array that specifies a different order for when -1000 (in A2) needs to be present.

so for the example above the desired output is :

 T   A1    A2 
0	45	-1000   % array is true and first time -1000 appears 
1	182	181  % array above is false 
2	29	-1000 % second time -1000 appears 
3	182	180
4	181	180

Any efficient ways to do this?

Your help will be greatly appreciated!

Answer 1

[Arun]

Hi Levi,

I understand that the objective is to sort the table in accordance with the value present in an array. A logical true value indicates that the table row should have value -1000. I assume that the number of rows with -1000 values and true value in the array are equal.

The following steps helps in achieving the desired outcome:

1. Identify the index values for rows containing -1000 and those with other values.
2. Generate pointers corresponding to the index values determined in step 1.
3. Examine the array values and populate the table rows accordingly.

Here is the code that helps to attain the desired output:

T = [0; 1; 2; 3; 4];
A1 = [182; 182; 181; 45; 29];
A2 = [181; 180; 180; -1000; -1000];
initialT = table(T, A1, A2);
array = logical([true false true false false]);
%find the rows with -1000 values
indexm1000 = find(initialT.A2 == -1000);
indexNot = setdiff([1:height(initialT)],indexm1000);
%pointers to track the order of -1000 and non -1000 rows
iindexm1000 = 1;
iindexNot = 1;
finalT = table(); % empty table to store the values in the required order.
%check if true place the row with -1000 value
for i = array
    %if true insert the row with -1000 value
    if(i)
        finalT(end+1,:) = initialT(indexm1000(iindexm1000),:);
        iindexm1000 = iindexm1000 +1;
    else
        finalT(end+1,:) = initialT(indexNot(iindexNot),:);
        iindexNot = iindexNot +1;
    end
end
disp(finalT);

    T    A1      A2  
    _    ___    _____

    3     45    -1000
    0    182      181
    4     29    -1000
    1    182      180
    2    181      180

For more information related to table please refer the documentation link: https://www.mathworks.com/help/matlab/tables.html

HTH