How to transform list with index numbers
MapIndexed[Append[#2, #] &, {1, 2, 1, 2, 1, 2}]
{{1, 1}, {2, 2}, {3, 1}, {4, 2}, {5, 1}, {6, 2}}
Also
MapIndexed[Reverse@Flatten[{##}] &, {1, 2, 1, 2, 1, 2}]
{{1, 1}, {2, 2}, {3, 1}, {4, 2}, {5, 1}, {6, 2}}
Transpose[{Range @ Length @ #, #}] &@{1, 2, 1, 2, 1, 2}
{{1, 1}, {2, 2}, {3, 1}, {4, 2}, {5, 1}, {6, 2}}
Module[{i = 1}, {i++, #} & /@ {1, 2, 1, 2, 1, 2}]
{{1, 1}, {2, 2}, {3, 1}, {4, 2}, {5, 1}, {6, 2}}
Thread[List[Range@Length@list, list]]
or
MapThread[{#, #2} &, {Range@Length@list, list}]