You can try this :
First, get the unique values of first column in a separate array using unique() function and define a number for each disease. With this you form a kind of 'rule' for each entry. Then run a loop on the main array and assign the numbers using the unique array.You can put this number in the third column of the main array. Then by sorting it according to the third column, you get continuous rows for the same disease, which in turn should group your node values as well.
