Sorting rows by column 1, and then sorting each subset of column 1 by column 2... i.e sort so X coordinates are ascending and then sort all values with the same X by Y

Hi all,

i have a point cloud stored as a 2D matrix, that is arranged as follows:

[X1, Y1, Z1;

X2, Y2, Z2;

X3, Y3, Z3;

X4, Y4, Z4;

X5, Y5, Z5;

.........]

I need to order it in terms of X first so have used sortrows(ARRAY,1)

but i now need to sort the subsiquent array in terms of Y, so for example if 5 X coordinates are the same, it would order them in terms of Y:

   -0.9793   19.6374   -0.4139
   -0.9793   19.7048   -0.2340
   -0.9793   19.7351   -0.4889
   -0.9793   19.8851   -0.2104
   -0.9793   19.7237   -0.2300
   -0.9793   19.6427   -0.4213
   -0.9793   19.6195   -0.2687
   -0.9793   19.7797   -0.2203
   -0.9793   20.1755   -0.3784
   -0.9793   19.6788   -0.4635
   -0.9792   19.6477   -0.4281
   -0.9792   20.1513   -0.4128
   -0.9792   19.6024   -0.2839
   -0.9792   20.1289   -0.4351
   -0.9792   20.1161   -0.2207
   -0.9792   20.1566   -0.2360
   -0.9792   19.9529   -0.2074
   -0.9792   20.1677   -0.3921
   -0.9792   20.0403   -0.4777

These would then be ordered in terms of Y, whilst preserving the X coordinates if that makes sense....

I'd appreciate any help!

Regards, Ben

Answer 1

[Arjun]

Hi,

As per my understanding, you want to sort the rows of the array first based on the column X and then on this you want to further sort on the basis of column Y. To address this need MATLAB has a function named sortrows, you can use this function with multiple columns specified. This will ensure that the sorting is hierarchical: first by the X values, and then by the Y values within each group of equal X values.

sortedPointCloud = sortrows(pointCloud, [1, 2]);
%Where column 1 is the X column and column 2 is the Y column

More about sortrows: https://www.mathworks.com/help/matlab/ref/double.sortrows.html

I hope this will help!