Performing computation using contents stored in a table

Hi,

I've the following table

t = [1 2 3 4 5 6 7 8 9]';
h = [2 3 4 5 6 7 8 9 10]';
value = [1 2 1 2 1 2 1 2 1]';
tbl = table(t,h,value);
tbl = mergevars(tbl,[1 2]);

I'm filtering the contents of the table using a search value. The contents present in the resulting table is used to perform some operations.

searchvalues = 1:10;
tic
for i = 1:length(searchvalues)
searchval = searchvalues(i);
newtable = tbl(any(tbl.Var1 == searchval, 2), :)
tochange = newtable.Var1(:, 2) == searchval;
newtable.Var1(tochange,:) = fliplr(newtable.Var1(tochange,:));
result(i) = sum((newtable.Var1(:,1) - newtable.Var1(:,2)).*newtable.value);   
end
toc
result

I'd like to ask for suggestions on how to speed up the steps carried out in for loop.

I tried the following,

searchvalues = 1:10;
tic
i = searchvalues;
newtable = tbl(any(tbl.Var1 == i, 2), :)
tochange = newtable.Var1(:, 2) == i;
newtable.Var1(tochange,:) = fliplr(newtable.Var1(tochange,:));
result(i) = sum((newtable.Var1(:,1) - newtable.Var1(:,2)).*newtable.value);   
end
toc
result

But, this didn't work.

EDIT: what happens in the for loop?

The following contents are stored in a table, in variable 'tbl',

        Var1                value
     ______________
    1    2                    1
    2    3                    2
    3    4                    1
    4    5                    2

I would like to do the following,

i = 2,

If the variable i is present in tbl.Var1, I would like to retain only those rows and delete the remining rows.

Example,

          Var1                value
     ______________
       1    2                    1
       2    3                    2

Also, if i is present in column 2 of Multico, the value in column 2 of tbl.Var1 , the columns are flipped

Th expected output is,

          Var1                value
     ______________
       2    1                    1
       2    3                    2

Then, I substract tbl(:,1) - tbl(:,2) , this results in a column vector. Sum of the dot product of this column vector and tbl.value is obtained, stored in variabl result.

I repeat the same for different values of i.

[darova]

Is it possible you to understand what are you trying to do in two words? Maybe you can make a scheme or simple drawing?

[Deepa Maheshvare]

Hi, Please check the edit and let me know if that's understandable.

[darova]

Yes, it's clear now. Thank you

Do you always operate on numbers? Why do you need table?

[Deepa Maheshvare]

Yes, I always operate on numbers . The data comes from an excel file, so I have imported as table. I could store in other formats if that will help in speeding up the opeartions carried out in for loop.

Answer 1

[darova]

Version without tables

var11 = [1 2 3 4 5 6 7 8 9]';
var12 = [2 3 4 5 6 7 8 9 10]';
value = [1 2 1 2 1 2 1 2 1]';
i = 2;
ind = (var11==i) | (var12==i);
% (without replacing columns) tbl(:,1) - tbl(:,2) the same as 
result = sum( (2*i-var11-var12).*value.*ind );

[Deepa Maheshvare]

Hi darova,

Thanks a lot for precisely answering my question. I'd like to know how the same can be implemented for anothe test case.

Instead of doing

newtable.Var1(:,1) - newtable.Var1(:,2) 

I have to use newtable.Var1(:,1) and newtable.Var1(:,2) as indices to perform the same operation on a variable.

i.e.

A(newtable.Var1(:,1)) - A(newtable.Var1(:,2))

here A is a column vector with numbers in it.

In this case, I'll not be able to do (2*i-var11-var12) .

Could you please suggest other alternatives?

[darova]

Try

idx = abs( newtable.Var1(:,1)) - A(newtable.Var1(:,2) );
A(ix)