Stop Canonical Ordering of Output List

Question

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

kglr · Accepted Answer

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

You can map Cases over the list of alternatives:
Join @@ Cases[{#, __}][m] & /@ (List @@ alternatives);

TableForm @ %

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

Michael E2 · Answer

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]]]

Stop Canonical Ordering of Output List

2 Answers

Add your own answers!

Ask a Question