How to publish/subscribe to an X,Y,Z array in ROS

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I am trying to publish and subscribe to an array containing X,Y,Z values that I find useful. These values are taken directly from a PointCloud<xyzi>.

The general format for the <float> array is:

my_array[x][y] = z;

However, I can't seem to find any useful tutorials for my setup. I saw multidimensional arrays, but I'm not sure how to apply them to this situation. From what I read, it doesn't seem like it would apply.

Thanks for your help!