if data(4) > 13 & data(4) < 15 blah blah elseif data(4) > 2 & data(4) < 4 other blah blah else that other thing end

Your if statement is only executed once - not once per element. While F(:,i)<50 returns an array of values, the if is either true or false; consequently, the next line is only executed once (either on all elements in G(:,i), or none of them).

For example, see this piece of code:

if(1 < [0 1 2]), disp('true'); end

It will produce no output, even though it is true for the third element. On the other hand,

if(1 < [2 3 4]), disp('true'); end

does produce output...

In general, the following:

1 < [0 1 2]

produces

0 0 1

Not sure why you say it doesn't work for < but it does work for ~=. Maybe there are no elements equal to 50, so it only "seems" to work?

In general, there is a better way to do what you want, with a single line:

G(F(:,2)<50,2)=1

This uses "logical indexing", and is much faster than looping. It will consider each element of F(:,2), and modify the corresponding element in G.

One final comment: it is not great practice to use the variable i since it has a built in value of sqrt(-1). If you have code anywhere that relies on it having that value, then accidentally overwriting it with any other value would break that. It's not the problem with your code today - but why set yourself up for a problem in the future.

find (lat >= 44 & lat <= 55)

see below for a demonstration Time = [1 2 3 4 5 6 7 8 9]'; Capacitance = [0.3 0.5 0.8 1 1.3 1.4 1.2 0.9 0.5]'; MyTable = table(Time,Capacitance) % delete variables, just to show that we work with the data from the table clearvars Time Capacitance % set a treshold value Treshold = 1; % use some logice to find the values larger then the treshold (if you want % to include it use >= instead of > KeepMe = MyTable.Capacitance > Treshold; % extract a part of the table using the logical array NewTable = MyTable( KeepMe , : )