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I'm working with the code below, which works well for my purposes; however, instead of the canonical ordering seen in the output, I want the output produced in the order I give in the Cases line of code. Any help is most appreciated.

ClearAll;
m = {{N11, "x"}, {N12, "y"}, {N19, "z"}, {N20, "w"}, {N41, 
    "exz"}, {N42, "jy"}, {N49, "br"}, {N50, "mew"}, {N61, "qr"}, {N62,
     "xqe"}, {N539, "ycf"}, {N551, "pyu"}, {N559, "wq"}, {N560, 
    "hra"}};
Cases[m, {N19 | N560 | N41 | N61 | N551 | N20 | N539, __}];
TableForm[%]

Output from the above code

N19 z
N20 w
N41 exz
N61 qr
N539 ycf
N551 pyu
N560 hra
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2 Answers 2

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alternatives = N19 | N560 | N41 | N61 | N551 | N20 | N539;

You can map Cases over the list of alternatives:

Join @@ Cases[{#, __}][m] & /@ (List @@ alternatives);

TableForm @ %

enter image description here

Alternatively, sort the output of Cases by the position in alternatives of the first column elements:

SortBy[PositionIndex[List @@ alternatives]@*First][Cases[m, {alternatives, __}]];

% // TableForm

enter image description here

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  • 1
    $\begingroup$ Many many thanks kglr; once again I very much appreciate you sharing your excellent skills! ... v/r ... prg $\endgroup$
    – user42700
    Feb 7, 2021 at 0:34
  • $\begingroup$ @PRG, my pleasure. Thank you for the accept. $\endgroup$
    – kglr
    Feb 7, 2021 at 0:39
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The cases will be found in the order they occur in m. If each case is unique, as in the example, the following can be used:

Sort[
 Cases[m, {N19 | N560 | N41 | N61 | N551 | N20 | N539, __}]
 ][[Ordering[N19 | N560 | N41 | N61 | N551 | N20 | N539]]]
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  • $\begingroup$ Michael E2 ... thank u very much!!! $\endgroup$
    – user42700
    Feb 7, 2021 at 15:59
  • $\begingroup$ @PRG You're welcome. :) $\endgroup$
    – Michael E2
    Feb 7, 2021 at 16:12

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