[GAP Forum] Comparison of Length of Lists of list

[Christopher Jefferson]

I would switch to doing this in two passes:

First get the length of the longest sublist:

Maximum(List(l, x -> Length(x));

Then get the lists of that length:

Filtered(l, x -> Length(x)=4);

If you aren't familiar with these notations (they are worth learning), you
could write out some loops instead:

maxlen := 0;
for i in [1..Length(l)] do
  maxlen := Maximum(maxlen, Length(l[i]));
od;

k := [];
for i in [1..Length(l)] do
  if Length(l[i]) = maxlen then
    Add(k, l[i]);
  fi;
od;



Or, we could loop directly over the members of l:

maxlen := 0;
for i in l do
  maxlen := Maximum(maxlen, Length(i));
od;

k := [];
  for i in l do
  if Length(i) = maxlen then
    Add(k, i);
  fi;
od;



On 10/10/2014 13:59, "Siddiqua Mazhar (PGR)" <s.mazhar at newcastle.ac.uk>
wrote:

>Dear Sir/Madam,
> Here I made changes in my previous email, sorry for inconvinience
>
>If I have a list let say
>a:=[[1,2,3],[4,5],[6,7,8,9],[10,11,12,],[13,14],[15,16,17,18]];
>
>I want to find the list of maximum length in it, or collection of list of
>max length from above
>
>For instance,  result:=[[6,7,8,9],[15,16,17,18]]; how can i find this
>result?
>
>here is one algorithm that I tried
>
>>Comparison:=function(a)
>>local i,k;
>>k:=[];
>>  for i in [1..(Length(a)-1)] do
>>     if Length(a[i])<Length(a[i+1]) then
>>         Add(k,a[i+1]);
>>      elif not a[i] in k then
>>          Add(k,a[i]);
>>     fi;
>>  od;
>>return k;
>>end;
>
>This program works, however , what if two list are of same length next to
>each other?
>for instance a:=[[1,2,3],[4,5],[6,7],[8,9,10]]?
>
>want this result:=[1,2,3],[8,9,10]
>
>or if a:=[[1,2],[3,4],[5,6]] in this case the result wouldl be the same
>as a because every list are of same length.
>
>Many thanks.
>
>Kind regards
>Siddiqua
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