Get indices for cells in an array that match a value, refer to the other column of data, put these into a new variable

I have m lots of 2 columns of data, length n, stored in a 2 x n x m array.

[x] = 2 x n x m doubles

I plot each data set on a graph, and allow the user to select the data point from n to plot across the m data sets. e.g. value_store = 520

How would I find the index of the data where value_store matches the data in column 1 of the 2 x n x m array, and use that to refer to the point I wish to plot in each series m?

For p = 1:m 
    % find which cell is equal to the user-selected value
    % refer to the other column of data
    % put this data into a new variable
end 

plot(y-axis_value_at_selected_data_points,m)

where m is the data sets from the original array

Thanks in advance for the help

Answer 1

[the cyclist]

x(:,:,1)==value_store

returns a 2 x n matrix identifying all the locations in the first "slice" (which contains all the "first columns" of your 3-D array) of x that equal value_store.