# Eliminate empty elements from a list with a specific pattern

I am really new in this patterns part of Mathematica. Basically what I need to do is eliminate null elements from a list but that has a specific name before the empty element. For example, my list is:

list={"a11-b11-{}", "a12-b11-{1}", "c11-d22-{}", "d33-c22-{2}"}


and I need to obtain

list={"a12-b11-{1}", "d33-c22-{2}"}


The list was created using

list =  Flatten[Table[ ToString[namea[[i]] <> "-" <> nameb[[j]] <> "-" <>
ToString[ Select[int[i, j, 0.5], Abs[#] == 0.5 &, 1]  ]],
{i, 1, 4}, {j, 1, 4}], 1]


and for some values it writtes {} because there is not a value equal to $$0.5$$. Until now I have been able to do it term by term as

list//."a11-b11-{}"-> Sequence[]


but the real list contains a lot of elements and could be almost impossible to do it that way to solve the problem. I think my main problem is that I am not sure how to specify the pattern search (something like " *-name " in gnu/linux). Is there a wise way to do this?. Thanks in advance.

• Have a look at DeleteCases and StringMatchQ or StringContainsQ. Apr 8, 2019 at 14:31
• I think it would be more efficient to first filter out the unwanted cases in the int function, and then construct strings only from the remaining ones. Apr 8, 2019 at 15:01
• @b.gatessucks Thank you, I will look those option in Mathematica.
– mors
Apr 8, 2019 at 15:07
• @Roman You are right, but I am new ih this cases stuf in Mathematica and I did no know how to do it when I created the list.
– mors
Apr 8, 2019 at 15:09

If the list elements are strings, as it appears after your comment, you can use Select with a string pattern:

list = {"a11-b11-{}", "a12-b11-{1}", "c11-d22-{}", "d33-c22-{2}"};
Select[list, Not@*StringMatchQ[__ ~~ "{}"]]


{"a12-b11-{1}", "d33-c22-{2}"}

You could also Select before making the strings:

L = DeleteCases[
Flatten[
Table[
{namea[[i]], nameb[[j]], Select[int[i, j, 0.5], Abs[#] == 0.5 &, 1]},
{i, 4}, {j, 4}],
1],
{_, _, {}}];


and then make these into strings:

StringRiffle[ToString /@ #, "-"] & /@ L


I can't check this because you didn't supply functioning code.

• Thank you, I forgot to specify the way the list is created. I create the list as 'list = Flatten[Table[ ToString[namea[[i]] <> "-" <> nameb[[j]] <> "-" <> ToString[ Select[int[i, j, 0.5], Abs[#] == 0.5 &, 1] ]], {i, 1, 4}, {j, 1, 4}], 1] '
– mors
Apr 8, 2019 at 14:39
• Thank you. The second part of your answer was really helpfull.
– mors
Apr 11, 2019 at 11:49

In 10.1, two functions were added to handle a pair of very common cases: StringStartsQ and StringEndsQ which return True if the string matches a pattern at the beginning or end, respectively. So, while Roman's answer gives you the full general form, most of the pattern can be eliminated by using

list = {"a11-b11-{}", "a12-b11-{1}", "c11-d22-{}", "d33-c22-{2}"};
Select[list, Not@*StringEndsQ["{}"]]