How to create corresponding equation in a column based on the value of previous column? (Similar to drag in Excel)

Hi all,

Imagine we have a 1000 x 3 matrix named A. I want to have a specific equation such as A(1,1) * by EquationA if the value in A(1,1) is less than 50 and A(1,1) * by EquationB if the value in A(1,1) is greater than or equal to 50. Then, drag this logic for the entire 1000 rows similar to Excel. How should I do this?

Answer 1

[Stephen23]

The MATLAB approach would be to use logical indexing:

https://www.mathworks.com/help/matlab/math/array-indexing.html

For example,assuming that your "equations" are actually vectorized functions:

Z = eqB(A(:,1));
X = A(:,1)<50; % logical vector
Z(X) = eqA(A(X,1))

[Wolfgang McCormack]

@Stephen Cobeldick thank you. So just a quick question, does the first line multiply the entire A's members by eqB? or just the ones above 50?

Now, in the last line, Z all those mathcing X condition will be multiplied by eqA. but is the final matrix a compiled matrix of all Z mutiplied by eqB and eqA? or should I compile/join it manually?

[Stephen23]

"So just a quick question, does the first line multiply the entire A's members by eqB? or just the ones above 50?"

All of them.

"but is the final matrix a compiled matrix of all Z mutiplied by eqB and eqA? or should I compile/join it manually?"

You do not need to join anything manually, the indexing already "joins" the data:

Z(X) = eqA...
% ^ this indexing combines the eqA data into the eqB data.