java - Grouping values by a common attribute in a matrix -


i'm having trouble in transforming 2-d matrix 2d array/list/vector based on common value of original matrix.

for example have ordered 2d_array of string(the code quite big) shown bellow.

string [][] 2d_array  =  { {1922, abc}, {1922, xpt}, {1954,abc}, {2001, sss}, {2001, asd}}; // array has "n" row

i transform/create following "output".

new_array = {{1922, abc, xpt}, {1954, abc}, {2001, sss, asd}};

in new array not matter how long number of columns be, long in same row accordingly "number"/date/index/etc.

try:

map<string, set<string>> res =    arrays.stream(2d_array)         .collect(groupingby(a -> a[0], mapping(a -> a[1], toset())));

you can convert map desired array if find array more convenient.


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