Counting number of particles in each position

Ok , so I have an array conatining particle trajectories from a random walk in which each column is a particle trajectory and it looks something like this for example

r = [1 3 4 5 6; 0 3 1 2 4; 2 4 5 6 7]

The particles have a fixed step and my goal is to find the number of particles in each possible position in every step in a very efficient way. I want to do this outside the for loop that generates the particle trajectories. I have a row vector conatining the possible particle positions for example

possteps = 1:10;

I want to use the approach used in this anwer

https://uk.mathworks.com/matlabcentral/answers/423714-count-number-of-times-value-occurs#answer_341152

but I am having trouble implementing it so that i get the particle counts for every step (for every row in r)

If anyone has any suggestions on how to do did effiiently for big arrays of r and possteps I would be very grateful.