How do I sort an array by only one column?

I have an array with the first column being x-coordinate, the second column being y-coordinate and then the next few columns being different values. I've used an if function so that all the y-coordinates are the same in the array but I then want to sort by x-coordinate (so my plot(x,y) is in order rather than jumping all over the place). The problem is that when I use the sort() function, it orders all my other columns too so the data is no longer associated with the correct coordinate.

This is a copy of the data unsorted.

This is after I've used the sort function. It also sorts column 3 which I don't want to happen. I want the 58.6480 value (column 3) to remain in the same row as the 20 value from column 1.

Answer 1

[dpb]

doc sortrows  

% ALWAYS read "See Also" when looking for related functions!!!
>> help sort
 sort   Sort in ascending or descending order.
    B = sort(A) sorts in ascending order.
...
    
    See also issorted, sortrows, min, max, mink, maxk.

[madhan ravi]

matrix(:,1)=sort(matrix(:,1))

[dpb]

>> A = [3 6 5; 7 -2 4; 1 0 -9]
A =
     3     6     5
     7    -2     4
     1     0    -9
>> A(:,1)=sort(A(:,1))
A =
     1     6     5
     3    -2     4
     7     0    -9
>> 

Now, while the other two columns aren't sorted, they don't match their associated data, either... :(

To do it this way, one would need something like--

[~,is]=sort(A(:,1);
A=A(is,:);

sortrows does the indexing/rearranging for you...

[madhan ravi]

Completely agree dpb, as far as I understand OP just wants to sort the first column and leave the rest intact, maybe I misunderstood the question.

[dpb]

"The problem is that when I use the sort() function, it orders all my other columns too so the data is no longer associated with the correct coordinate."

[madhan ravi]

+1, Yes I reread it, now its clear. Thank you dpb :), sorry for the inconvenience.

[dpb]

'S ok...we all have our moments... :) I certainly "whiff" often enough.

[madhan ravi]

:)