Avoiding unpacking an array when altering its dimension












6












$begingroup$


I am trying to flatten a matrix from 3-dimensional to 2-dimensional one.



The original one has dimension for example {10,120,120}:



list1 = RandomReal[1, {10, 120, 120}];


I want to convert it to a new matrix with {10,120*120} dimension. I am using:



On["Packing"]  (*For checking if exist unpacked arrays *)  

Flatten[Map[Flatten, {list1}, {-3}], 1];


But this will generate unpacked array. How should I avoid this issue?






list-manipulation packed-arrays







share|improve this question











$endgroup$








  • 4




    $begingroup$
    Try Flatten[list1, {{1}, {2, 3}}].
    $endgroup$
    – J. M. is computer-less♦
    yesterday










  • $begingroup$
    Thanks, it works!
    $endgroup$
    – cj9435042
    yesterday
















6












$begingroup$


I am trying to flatten a matrix from 3-dimensional to 2-dimensional one.



The original one has dimension for example {10,120,120}:



list1 = RandomReal[1, {10, 120, 120}];


I want to convert it to a new matrix with {10,120*120} dimension. I am using:



On["Packing"]  (*For checking if exist unpacked arrays *)  

Flatten[Map[Flatten, {list1}, {-3}], 1];


But this will generate unpacked array. How should I avoid this issue?






list-manipulation packed-arrays







share|improve this question











$endgroup$








  • 4




    $begingroup$
    Try Flatten[list1, {{1}, {2, 3}}].
    $endgroup$
    – J. M. is computer-less♦
    yesterday










  • $begingroup$
    Thanks, it works!
    $endgroup$
    – cj9435042
    yesterday














6












6








6


1



$begingroup$


I am trying to flatten a matrix from 3-dimensional to 2-dimensional one.



The original one has dimension for example {10,120,120}:



list1 = RandomReal[1, {10, 120, 120}];


I want to convert it to a new matrix with {10,120*120} dimension. I am using:



On["Packing"]  (*For checking if exist unpacked arrays *)  

Flatten[Map[Flatten, {list1}, {-3}], 1];


But this will generate unpacked array. How should I avoid this issue?






list-manipulation packed-arrays







share|improve this question











$endgroup$




I am trying to flatten a matrix from 3-dimensional to 2-dimensional one.



The original one has dimension for example {10,120,120}:



list1 = RandomReal[1, {10, 120, 120}];


I want to convert it to a new matrix with {10,120*120} dimension. I am using:



On["Packing"]  (*For checking if exist unpacked arrays *)  

Flatten[Map[Flatten, {list1}, {-3}], 1];


But this will generate unpacked array. How should I avoid this issue?






list-manipulation packed-arrays




list-manipulation packed-arrays






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited yesterday









m_goldberg

87.4k872198




87.4k872198










asked yesterday









cj9435042cj9435042

37616




37616








  • 4




    $begingroup$
    Try Flatten[list1, {{1}, {2, 3}}].
    $endgroup$
    – J. M. is computer-less♦
    yesterday










  • $begingroup$
    Thanks, it works!
    $endgroup$
    – cj9435042
    yesterday














  • 4




    $begingroup$
    Try Flatten[list1, {{1}, {2, 3}}].
    $endgroup$
    – J. M. is computer-less♦
    yesterday










  • $begingroup$
    Thanks, it works!
    $endgroup$
    – cj9435042
    yesterday








4




4




$begingroup$
Try Flatten[list1, {{1}, {2, 3}}].
$endgroup$
– J. M. is computer-less♦
yesterday




$begingroup$
Try Flatten[list1, {{1}, {2, 3}}].
$endgroup$
– J. M. is computer-less♦
yesterday












$begingroup$
Thanks, it works!
$endgroup$
– cj9435042
yesterday




$begingroup$
Thanks, it works!
$endgroup$
– cj9435042
yesterday










1 Answer
1






active

oldest

votes


















14












$begingroup$

An alternative to using Flatten as in the comments is to use ArrayReshape. For large arrays, ArrayReshape should be significantly faster. For example:



list1 = RandomReal[1, {10, 1200, 1200}];


Comparison:



r1 = Flatten[list1, {{1}, {2, 3}}]; //RepeatedTiming

r2 = ArrayReshape[list1, {10, 1200 1200}]; //RepeatedTiming



r1 === r2



{0.120, Null}



{0.025, Null}



True







share|improve this answer









$endgroup$













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    active

    oldest

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    14












    $begingroup$

    An alternative to using Flatten as in the comments is to use ArrayReshape. For large arrays, ArrayReshape should be significantly faster. For example:



    list1 = RandomReal[1, {10, 1200, 1200}];


    Comparison:



    r1 = Flatten[list1, {{1}, {2, 3}}]; //RepeatedTiming
    
r2 = ArrayReshape[list1, {10, 1200 1200}]; //RepeatedTiming
    

    
r1 === r2



    {0.120, Null}



    {0.025, Null}



    True







    share|improve this answer









    $endgroup$


















      14












      $begingroup$

      An alternative to using Flatten as in the comments is to use ArrayReshape. For large arrays, ArrayReshape should be significantly faster. For example:



      list1 = RandomReal[1, {10, 1200, 1200}];


      Comparison:



      r1 = Flatten[list1, {{1}, {2, 3}}]; //RepeatedTiming
      
r2 = ArrayReshape[list1, {10, 1200 1200}]; //RepeatedTiming
      

      
r1 === r2



      {0.120, Null}



      {0.025, Null}



      True







      share|improve this answer









      $endgroup$
















        14












        14








        14





        $begingroup$

        An alternative to using Flatten as in the comments is to use ArrayReshape. For large arrays, ArrayReshape should be significantly faster. For example:



        list1 = RandomReal[1, {10, 1200, 1200}];


        Comparison:



        r1 = Flatten[list1, {{1}, {2, 3}}]; //RepeatedTiming
        
r2 = ArrayReshape[list1, {10, 1200 1200}]; //RepeatedTiming
        

        
r1 === r2



        {0.120, Null}



        {0.025, Null}



        True







        share|improve this answer









        $endgroup$



        An alternative to using Flatten as in the comments is to use ArrayReshape. For large arrays, ArrayReshape should be significantly faster. For example:



        list1 = RandomReal[1, {10, 1200, 1200}];


        Comparison:



        r1 = Flatten[list1, {{1}, {2, 3}}]; //RepeatedTiming
        
r2 = ArrayReshape[list1, {10, 1200 1200}]; //RepeatedTiming
        

        
r1 === r2



        {0.120, Null}



        {0.025, Null}



        True








        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered yesterday









        Carl WollCarl Woll

        69.2k392179




        69.2k392179






























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