Using patterns in ReplaceAll to extract elements from tuples at arbitrary depths

Question

Please consider the following:

I need to extract from MyList all last parts of each 3-tuple.

MyList={
         {{0.`, 2, 5}},
         {{0.`, 1, 8},{10.`, 10, 10},{10.`, 6, 2.5}},
         {{0.`, 1.25, 10},{0.`, 8.9, 100}}
       };

I tried to apply the following but it did not work:

MyList /. {a_Number, b_Number, c_Number} :> c

Please note, that a,b and c must be of Number, otherwise the last 3-tuple of MyList[[2]] would be extracted to, since it MyList[[2]] itself represents a 3-tuple.

The result must be:

{{5},{8,10,2.5},{10,100}}

Answer 1

Any time you write a pattern, you should stop and ask yourself a couple of questions — "Is this really a Head?", "Does this pattern test return True or False"... Number, which represents a real/integer in Read is different from ?NumericQ, which is a pattern test. In this case, the latter is what you need.

MyList /. {__, x_?NumericQ} :> x
(* {{5}, {8, 10, 2.5}, {10, 100}} *)

Alternately, you could also map Last to the appropriate level in your list:

Map[Last, MyList, {Depth[list] - 2}]
(* {{5}, {8, 10, 2.5}, {10, 100}} *)

Answer 2

MyList /. {_, _, c_?NumberQ} :> c

{{5}, {8, 10, 2.5}, {10, 100}}