4
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modified list

From a numerical evaluation I get examplary result

    list = { {{{5.65594, 0.01, 1.8064, 2.96708}}, {{5.96278, 0.01, 1.9062,
      2.96321}}, {{14.4801, 0.01, 4.8004, 0.232071}, {15.1634, 0.01, 
     4.8004, 1.27159}, {14.7847, 0.01, 4.8004, 2.70053}}, {{6.2694, 
     0.01, 2.006, 2.9591}}, {{14.6342, 0.01, 4.9002, 
     0.223376}, {15.4072, 0.01, 4.9002, 1.31633}, {15.0859, 0.01, 
     4.9002, 2.68233}}, {{14.7904, 0.01, 5., 0.215253}, {15.6555, 
     0.01, 5., 1.36177}, {15.3868, 0.01, 5., 2.66285}}} ,
  {{{5.65594, 0.01, 1.8064, 2.96708}}}
  }

list contains sublists of length 4. grouped to one or three elements.

I tried Select[list,Length[#]==1&] without success

My question:

  • How can I extract list in a sublist, which only contains one sublist of four elements.
  • How can I extract list in a sublist, which only contains three sublists of four elements.

Thanks!

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4 Answers 4

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3
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To also answer the revised question:

Sublists of length 1

sel = Select[#, Length[#] == 1 &] & /@ list

{{{{5.65594, 0.01, 1.8064, 2.96708}}, {{5.96278, 0.01, 1.9062, 2.96321}}, {{6.2694, 0.01, 2.006, 2.9591}}}, {{{5.65594, 0.01, 1.8064, 2.96708}}}}

Sublists of length 1 with 4 elements (all of them have 4 elements)

Cases[sel, {Repeated[_, {4}]}, -1]

{{5.65594, 0.01, 1.8064, 2.96708}, {5.96278, 0.01, 1.9062, 2.96321}, {6.2694, 0.01, 2.006, 2.9591}, {5.65594, 0.01, 1.8064, 2.96708}}

4 sublists with 4 elements don't exist:

Select[#, Length[#] == 4 &] & /@ list

{{}, {}}

But there are three sublists with 4 elements

sub = Select[#, Length[#] == 3 &] & /@ list

{{{{14.4801, 0.01, 4.8004, 0.232071}, {15.1634, 0.01, 4.8004, 1.27159}, {14.7847, 0.01, 4.8004, 2.70053}}, {{14.6342, 0.01, 4.9002, 0.223376}, {15.4072, 0.01, 4.9002, 1.31633}, {15.0859, 0.01, 4.9002, 2.68233}}, {{14.7904, 0.01, 5., 0.215253}, {15.6555, 0.01, 5., 1.36177}, {15.3868, 0.01, 5., 2.66285}}}, {}}

Map[Length, sub, {3}]

{{{4, 4, 4}, {4, 4, 4}, {4, 4, 4}}, {}}

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2
  • $\begingroup$ (+1) Also (operator form): Select[Length[#] == 1 &] /@ list $\endgroup$
    – user1066
    Commented Jan 2 at 5:02
  • $\begingroup$ Thanks, 1066, of course :) $\endgroup$
    – eldo
    Commented Jan 2 at 7:40
3
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Sublists of length 1

sel = Select[list[[1]], Length[#] == 1 &]

{{{5.65594, 0.01, 1.8064, 2.96708}}, {{5.96278, 0.01, 1.9062, 2.96321}}, {{6.2694, 0.01, 2.006, 2.9591}}}

Sublists of length 1 with 4 elements (all of them have 4 elements)

 Cases[sel, {Repeated[_, {4}]}, {2}]

{{5.65594, 0.01, 1.8064, 2.96708}, {5.96278, 0.01, 1.9062, 2.96321}, {6.2694, 0.01, 2.006, 2.9591}}

4 sublists with 4 elements don't exist:

Map[Length, Select[list[[1]], Length[#] == 4 &], {2}]

{}

But there are 3 sublists, all of them with 4 elements:

Map[Length, Select[list[[1]], Length[#] == 3 &], {2}]

{{4, 4, 4}, {4, 4, 4}, {4, 4, 4}}

Here they are:

Select[list[[1]], Length[#] == 3 &]

{{{14.4801, 0.01, 4.8004, 0.232071}, {15.1634, 0.01, 4.8004, 1.27159}, {14.7847, 0.01, 4.8004, 2.70053}}, {{14.6342, 0.01, 4.9002, 0.223376}, {15.4072, 0.01, 4.9002, 1.31633}, {15.0859, 0.01, 4.9002, 2.68233}}, {{14.7904, 0.01, 5., 0.215253}, {15.6555, 0.01, 5., 1.36177}, {15.3868, 0.01, 5., 2.66285}}}

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1
  • $\begingroup$ Thanks for your answer. My underlying problem is a bit more complicated, because {list[[1]]}!=list . I have to modify my question $\endgroup$
    – Ulrich Neumann
    Commented Dec 31, 2023 at 10:47
3
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An alternative to handling additional braces is to use Catenate and then use Position and Extract:

list = {{{{5.65594, 0.01, 1.8064, 2.96708}}, {{5.96278, 0.01, 1.9062, 2.96321}}, 
        {{14.4801, 0.01, 4.8004, 0.232071}, {15.1634, 0.01, 4.8004, 1.27159}, 
        {14.7847, 0.01, 4.8004, 2.70053}}, {{6.2694,0.01, 2.006, 2.9591}}, 
        {{14.6342, 0.01, 4.9002, 0.223376}, {15.4072, 0.01, 4.9002, 1.31633}, 
        {15.0859, 0.01, 4.9002, 2.68233}}, {{14.7904, 0.01, 5., 0.215253}, 
        {15.6555, 0.01, 5., 1.36177}, {15.3868, 0.01, 5., 2.66285}}}};

        Union@Extract[#, Position[#, m_ /; Length[m] == 3]] &@Catenate@list

        (*{{{14.4801, 0.01, 4.8004, 0.232071}, {15.1634, 0.01, 4.8004, 1.27159}, 
         {14.7847, 0.01, 4.8004, 2.70053}}, {{14.6342, 0.01, 4.9002, 0.223376}, 
         {15.4072, 0.01, 4.9002, 1.31633}, {15.0859, 0.01, 4.9002, 2.68233}}, 
         {{14.7904, 0.01, 5., 0.215253}, {15.6555, 0.01, 5., 1.36177}, 
         {15.3868, 0.01, 5., 2.66285}}}*)
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0
2
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Did you intentionally write double braces? If yes, you need to take care of this. E.g. you may write:

list = {{{{5.65594, 0.01, 1.8064, 2.96708}}, {{5.96278, 0.01, 1.9062, 
      2.96321}}, {{14.4801, 0.01, 4.8004, 0.232071}, {15.1634, 0.01, 
      4.8004, 1.27159}, {14.7847, 0.01, 4.8004, 2.70053}}, {{6.2694, 
      0.01, 2.006, 2.9591}}, {{14.6342, 0.01, 4.9002, 
      0.223376}, {15.4072, 0.01, 4.9002, 1.31633}, {15.0859, 0.01, 
      4.9002, 2.68233}}, {{14.7904, 0.01, 5., 0.215253}, {15.6555, 
      0.01, 5., 1.36177}, {15.3868, 0.01, 5., 2.66285}}}};

Select[list[[1]], (Length[#] == 1) &]

{{{5.65594, 0.01, 1.8064, 2.96708}}, {{5.96278, 0.01, 1.9062, 
   2.96321}}, {{6.2694, 0.01, 2.006, 2.9591}}}

Further, you do not have sublists of length 4, but of length 3. To get these, you may write:

Select[list[[1]], (Length[#] == 3) &]

{{{14.4801, 0.01, 4.8004, 0.232071}, {15.1634, 0.01, 4.8004, 
   1.27159}, {14.7847, 0.01, 4.8004, 2.70053}}, {{14.6342, 0.01, 
   4.9002, 0.223376}, {15.4072, 0.01, 4.9002, 1.31633}, {15.0859, 
   0.01, 4.9002, 2.68233}}, {{14.7904, 0.01, 5., 0.215253}, {15.6555, 
   0.01, 5., 1.36177}, {15.3868, 0.01, 5., 2.66285}}}

Another possibility is to use Select as an operator like:

Select[Length[#] == 1 &] /@ list

{{{{5.65594, 0.01, 1.8064, 2.96708}}, {{5.96278, 0.01, 1.9062, 
    2.96321}}, {{6.2694, 0.01, 2.006, 2.9591}}}}
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1
  • $\begingroup$ The double curly brakets came from Table evaluation. Probably my example is to simple, because my underlying problem has a more complicated structure with {list[[1]]}!=list $\endgroup$
    – Ulrich Neumann
    Commented Dec 31, 2023 at 10:43

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