How to select rows based on the entry value of the first column

Question

Data={{0,5678},{0,5654},{1,87675},{2,243},{2,257},{1,9790},{0,7688},{1,97779},{0,6858}}

Given a data set similar to the above, how can I select rows where the first column entry is a number that I specify, and the following row is a row is where the first column entry is another number that I specify, and only alternating first column entries, for instance
Choose 0
Choose 1
I'd like the output to be
{{0,5678},{1,87675},{0,7688},{1,97779}}

Or if I do
Choose 1
Choose 2
I'd like the output to be
{{1,87675},{2,243},}

etc
So far I have
Cases[Data,{n_,_}/;n>=1]

This doesn't quite do it, but it's a start. Thanks!

kglr · Answer

SequenceCases
Join @@ SequenceCases[data, {{0, _}, {1, _}}]

{{0, 5654}, {1, 87675}, {0, 7688}, {1, 97779}}

Join @@ SequenceCases[data, {{1, _}, {2, _}}]

{{1, 87675}, {2, 243}}

SequencePosition + Part
Join @@ (data[[#]] & /@ SequencePosition[data[[All, 1]], {0, 1}])

{{0, 5654}, {1, 87675}, {0, 7688}, {1, 97779}}

Join @@ (data[[#]] & /@ SequencePosition[data[[All, 1]], {1, 2}])

{{1, 87675}, {2, 243}}

Split + Select
Join @@ Select[Length @ # >= 2 &] @ Split[data, #[[1]] == 0 && #2[[1]] == 1 &]

{{0, 5654}, {1, 87675}, {0, 7688}, {1, 97779}}

Join @@ Select[Length @ # >= 2 &]@ Split[data, #[[1]] == 1 && #2[[1]] == 2 &]

{{1, 87675}, {2, 243}}

Partition + Select
Join @@ Select[#[[All, 1]] == {0, 1} &] @ Partition[data, 2, 1]

{{0, 5654}, {1, 87675}, {0, 7688}, {1, 97779}}

Join @@ Select[#[[All, 1]] == {1, 2} &] @ Partition[data, 2, 1]

{{1, 87675}, {2, 243}}

BlockMap
BlockMap[If[#[[All, 1]] == {0, 1}, Sequence @@ #, Nothing] &, data, 2, 1]

{{0, 5654}, {1, 87675}, {0, 7688}, {1, 97779}}

BlockMap[If[#[[All, 1]] == {1, 2}, Sequence @@ #, Nothing] &, data, 2, 1]

{{1, 87675}, {2, 243}}

How to select rows based on the entry value of the first column

One Answer

`SequenceCases`

`SequencePosition` + `Part`

`Split` + `Select`

`Partition` + `Select`

`BlockMap`

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