How do I sort an array by only one column?
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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.
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dpb
2019-3-17
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.
7 个评论
madhan ravi
2019-3-17
matrix(:,1)=sort(matrix(:,1))
dpb
2019-3-17
>> 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
2019-3-17
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
2019-3-17
"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
2019-3-17
编辑：madhan ravi
2019-3-17
+1, Yes I reread it, now its clear. Thank you dpb :), sorry for the inconvenience.
dpb
2019-3-17
'S ok...we all have our moments... :) I certainly "whiff" often enough.
madhan ravi
2019-3-18
:)
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