COnsider a list
table = {{x1,y1,z1,t1},{x2,y2,z2,t2},...}
How to remove duplicates having the same values of {y,z} (say, {1,2,3,5},{99,2,3,9})? It is not important for me which exactly row will be remained.
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You can use DeleteDuplicatesBy
DeleteDuplicatesBy[#[[{2, 3}]]&] @ table
Example:
table = RandomInteger[3, {7, 4}]
{{1, 0, 1, 0}, {0, 0, 1, 1}, {0, 1, 0, 0}, {0, 2, 3, 0}, {3, 0, 1, 2}, {2, 3, 3, 0}, {3, 0, 1, 3}}
DeleteDuplicatesBy[#[[{2, 3}]] &] @table
{{1, 0, 1, 0}, {0, 1, 0, 0}, {0, 2, 3, 0}, {2, 3, 3, 0}}
Alternatively, you can use Union:
Union[table, SameTest -> (#[[{2, 3}]] == #2[[{2, 3}]] &)]
{{0, 0, 1, 1}, {0, 1, 0, 0}, {0, 2, 3, 0}, {2, 3, 3, 0}}
Note that DeleteDuplicatesBy keeps the elements that appear early in the original list while Union sorts the list.
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1$\begingroup$ Just to add: for large lists,
DeleteDuplicatesByis also significantly faster than usingUnionwithSameTestsince it does not have to run the test on each possible pair. If you want the output sorted, it's probably better to useDeleteDuplicatesByand thenSort. $\endgroup$ – Sjoerd Smit Jun 25 at 11:19
