Hi, I want to cluster my plots into two groups; similar group and the other

Each of my plot has four lines, so in here similar group means the group of plots that 4 lines in the plot show similar pattern.

My problem is how can I quantify the similarity between four lines in each plot. If I can quantify it, then I can set a threshold value and cluster it. (still, it could be an ambiguous but I guess if I can quantify similarity, the problem would be easier to solve than just clustering by seeing all the graph) 

I digitized plots and tabulated like

A   B    C    D   ...

5  10   50   70 ...

Is there any method to quantify similarity between 4 lines in the plot?

Similar questions and discussions