I'm trying to define a pattern that will match lists of lists, where the inner lists contains only numbers (I want the sum of each list). Like this
{{1, 2}, {3, 4}}
But not like this
{1, {1, 3},{{3}}}
Why this is not working?
Clear[foo];
foo[x : {v___List}] := Plus @@@ x /; VectorQ[v, NumberQ]
Thank you!
ClearAll[foo];
foo[x : {___List?(VectorQ[#, NumberQ] &)}] := Plus @@@ x
foo[{{1, 2}, {2, 3, 4}}]
{3, 9}
foo[{{1, 2}, {{3}}}]
foo[{{1, 2}, {{3}}}]
Note: You need to use NumericQ in place of NumberQ if you want foo[{{1, 2}, {2, 3, π}}] to return {3, 2 + 3 π}.
Another approach is to use Total, with a condition to forbid it from totaling entries with a single term:
f[x_] := If[Length[x] > 1, Total[x], x]
For instance:
f /@ {{1, 2}, {2, 3, 4}}
{3, 9}
f /@ {{1, 2}, {2, 3, 4}, {{3}}}
{3, 9, {{3}}}
VectorQ[v, NumberQ]forv=Sequence[{1, 2}, {3, 4}]becomesVectorQ[{1, 2}, {3, 4}, NumberQ]thus you get the error messageVectorQ::argt: VectorQ called with **3** arguments; 1 or 2 arguments are expected.$\endgroup$