Is there a foreach in MATLAB If so how does it behave if the underlying data changes

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Is there a foreach structure in MATLAB   If so  what happens if the underlying data changes  i e  if objects are added to the set

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As of today  Feb 27   there is a new For-Each toolbox on the MATLAB File Exchange that accomplishes the concept of foreach  foreach is not a part of the MATLAB language but use of this toolbox gives us the ability to emulate what foreach would do

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MATLAB s FOR loop is static in nature  you cannot modify the loop variable between iterations  unlike the for initialization condition increment  loop structure in other languages  This means that the following code always prints 1  2  3  4  5 regardless of the value of B   A   1 5   for i   A     A   B      disp i   end   If you want to be able to respond to changes in the data structure during iterations  a WHILE loop may be more appropriate --- you ll be able to test the loop condition at every iteration  and set the value of the loop variable s  as you wish   n   10  f   n  while n  gt  1     n   n-1      f   f n  end disp   n      num2str f      Btw  the for-each loop in Java  and possibly other languages  produces unspecified behavior when the data structure is modified during iteration  If you need to modify the data structure  you should use an appropriate Iterator instance which allows the addition and removal of elements in the collection you are iterating  The good news is that MATLAB supports Java objects  so you can do something like this   A   java util ArrayList    A add 1   A add 2   A add 3   A add 4   A add 5    itr   A listIterator     while itr hasNext        k   itr next        disp k          modify data structure while iterating     itr remove        itr add k    end

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Zach is correct about the direct answer to the question   An interesting side note is that the following two loops do not execute the same   for i 1 10000     do something end for i  1 10000      do something end   The first loop creates a variable i that is a scalar and it iterates it like a C for loop   Note that if you modify i in the loop body  the modified value will be ignored  as Zach says   In the second case  Matlab creates a 10k-element array  then it walks all elements of the array     What this means is that  for i 1 inf     do something end   works  but   for i  1 inf      do something end   does not  because this one would require allocating infinite memory    See Loren s blog for details   Also note that you can iterate over cell arrays

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MATLAB s FOR loop is static in nature  you cannot modify the loop variable between iterations  unlike the for initialization condition increment  loop structure in other languages  This means that the following code always prints 1  2  3  4  5 regardless of the value of B   A   1 5   for i   A     A   B      disp i   end   If you want to be able to respond to changes in the data structure during iterations  a WHILE loop may be more appropriate --- you ll be able to test the loop condition at every iteration  and set the value of the loop variable s  as you wish   n   10  f   n  while n  gt  1     n   n-1      f   f n  end disp   n      num2str f      Btw  the for-each loop in Java  and possibly other languages  produces unspecified behavior when the data structure is modified during iteration  If you need to modify the data structure  you should use an appropriate Iterator instance which allows the addition and removal of elements in the collection you are iterating  The good news is that MATLAB supports Java objects  so you can do something like this   A   java util ArrayList    A add 1   A add 2   A add 3   A add 4   A add 5    itr   A listIterator     while itr hasNext        k   itr next        disp k          modify data structure while iterating     itr remove        itr add k    end

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ooh  neat question   Matlab s for loop takes a matrix as input and iterates over its columns  Matlab also handles practically everything by value  no pass-by-reference  so I would expect that it takes a snapshot of the for-loop s input so it s immutable   here s an example which may help illustrate    gt  gt  A   zeros 4   A      1 16  A         1     5     9    13      2     6    10    14      3     7    11    15      4     8    12    16   gt  gt  i   1  for col   A  disp col    A   i    i  i   i   1  end       1     2     3     4       5     6     7     8       9    10    11    12      13    14    15    16   gt  gt  A  A         1     2     3     4      1     2     3     4      1     2     3     4      1     2     3     4

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ooh  neat question   Matlab s for loop takes a matrix as input and iterates over its columns  Matlab also handles practically everything by value  no pass-by-reference  so I would expect that it takes a snapshot of the for-loop s input so it s immutable   here s an example which may help illustrate    gt  gt  A   zeros 4   A      1 16  A         1     5     9    13      2     6    10    14      3     7    11    15      4     8    12    16   gt  gt  i   1  for col   A  disp col    A   i    i  i   i   1  end       1     2     3     4       5     6     7     8       9    10    11    12      13    14    15    16   gt  gt  A  A         1     2     3     4      1     2     3     4      1     2     3     4      1     2     3     4

User · Answer

As of today  Feb 27   there is a new For-Each toolbox on the MATLAB File Exchange that accomplishes the concept of foreach  foreach is not a part of the MATLAB language but use of this toolbox gives us the ability to emulate what foreach would do

User · Answer

Let s say you have an array of data   n    1    2   3   4   6   12  18  51  69  81      then you can  foreach  it like this   for i   n  i  end   This will echo every element in n  but replacing the i with more interesting stuff is also possible of course

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I think this is what the OP really wants   array   -1 0 1 10  for i 1 numel array      disp array i   end

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Let s say you have an array of data   n    1    2   3   4   6   12  18  51  69  81      then you can  foreach  it like this   for i   n  i  end   This will echo every element in n  but replacing the i with more interesting stuff is also possible of course

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I think this is what the OP really wants   array   -1 0 1 10  for i 1 numel array      disp array i   end

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The MATLAB for loop basically allows huge flexibility  including the foreach functionality  Here some examples    1  Define start  increment and end index  for test   1 3 9    test end   2  Loop over vector  for test    1  3  4     test end   3  Loop over string  for test    hello     test end   4  Loop over a one-dimensional cell array  for test     hello   42  datestr now   1 3     test end   5  Loop over a two-dimensional cell array  for test     hello  42 datestr now     world  43 datestr now 1      test 1        test 2     disp  ---   end   6  Use fieldnames of structure arrays  s a   1 3   s b   10     for test   fieldnames s      s  cell2mat test   end

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Zach is correct about the direct answer to the question   An interesting side note is that the following two loops do not execute the same   for i 1 10000     do something end for i  1 10000      do something end   The first loop creates a variable i that is a scalar and it iterates it like a C for loop   Note that if you modify i in the loop body  the modified value will be ignored  as Zach says   In the second case  Matlab creates a 10k-element array  then it walks all elements of the array     What this means is that  for i 1 inf     do something end   works  but   for i  1 inf      do something end   does not  because this one would require allocating infinite memory    See Loren s blog for details   Also note that you can iterate over cell arrays

User · Answer

Zach is correct about the direct answer to the question   An interesting side note is that the following two loops do not execute the same   for i 1 10000     do something end for i  1 10000      do something end   The first loop creates a variable i that is a scalar and it iterates it like a C for loop   Note that if you modify i in the loop body  the modified value will be ignored  as Zach says   In the second case  Matlab creates a 10k-element array  then it walks all elements of the array     What this means is that  for i 1 inf     do something end   works  but   for i  1 inf      do something end   does not  because this one would require allocating infinite memory    See Loren s blog for details   Also note that you can iterate over cell arrays

User · Answer

Zach is correct about the direct answer to the question   An interesting side note is that the following two loops do not execute the same   for i 1 10000     do something end for i  1 10000      do something end   The first loop creates a variable i that is a scalar and it iterates it like a C for loop   Note that if you modify i in the loop body  the modified value will be ignored  as Zach says   In the second case  Matlab creates a 10k-element array  then it walks all elements of the array     What this means is that  for i 1 inf     do something end   works  but   for i  1 inf      do something end   does not  because this one would require allocating infinite memory    See Loren s blog for details   Also note that you can iterate over cell arrays

User · Answer

If you are trying to loop over a cell array and apply something to each element in the cell  check out cellfun   There s also arrayfun  bsxfun  and structfun which may simplify your program

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MATLAB s FOR loop is static in nature  you cannot modify the loop variable between iterations  unlike the for initialization condition increment  loop structure in other languages  This means that the following code always prints 1  2  3  4  5 regardless of the value of B   A   1 5   for i   A     A   B      disp i   end   If you want to be able to respond to changes in the data structure during iterations  a WHILE loop may be more appropriate --- you ll be able to test the loop condition at every iteration  and set the value of the loop variable s  as you wish   n   10  f   n  while n  gt  1     n   n-1      f   f n  end disp   n      num2str f      Btw  the for-each loop in Java  and possibly other languages  produces unspecified behavior when the data structure is modified during iteration  If you need to modify the data structure  you should use an appropriate Iterator instance which allows the addition and removal of elements in the collection you are iterating  The good news is that MATLAB supports Java objects  so you can do something like this   A   java util ArrayList    A add 1   A add 2   A add 3   A add 4   A add 5    itr   A listIterator     while itr hasNext        k   itr next        disp k          modify data structure while iterating     itr remove        itr add k    end

User · Answer

MATLAB s FOR loop is static in nature  you cannot modify the loop variable between iterations  unlike the for initialization condition increment  loop structure in other languages  This means that the following code always prints 1  2  3  4  5 regardless of the value of B   A   1 5   for i   A     A   B      disp i   end   If you want to be able to respond to changes in the data structure during iterations  a WHILE loop may be more appropriate --- you ll be able to test the loop condition at every iteration  and set the value of the loop variable s  as you wish   n   10  f   n  while n  gt  1     n   n-1      f   f n  end disp   n      num2str f      Btw  the for-each loop in Java  and possibly other languages  produces unspecified behavior when the data structure is modified during iteration  If you need to modify the data structure  you should use an appropriate Iterator instance which allows the addition and removal of elements in the collection you are iterating  The good news is that MATLAB supports Java objects  so you can do something like this   A   java util ArrayList    A add 1   A add 2   A add 3   A add 4   A add 5    itr   A listIterator     while itr hasNext        k   itr next        disp k          modify data structure while iterating     itr remove        itr add k    end

User · Answer

ooh  neat question   Matlab s for loop takes a matrix as input and iterates over its columns  Matlab also handles practically everything by value  no pass-by-reference  so I would expect that it takes a snapshot of the for-loop s input so it s immutable   here s an example which may help illustrate    gt  gt  A   zeros 4   A      1 16  A         1     5     9    13      2     6    10    14      3     7    11    15      4     8    12    16   gt  gt  i   1  for col   A  disp col    A   i    i  i   i   1  end       1     2     3     4       5     6     7     8       9    10    11    12      13    14    15    16   gt  gt  A  A         1     2     3     4      1     2     3     4      1     2     3     4      1     2     3     4

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If you are trying to loop over a cell array and apply something to each element in the cell  check out cellfun   There s also arrayfun  bsxfun  and structfun which may simplify your program

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When iterating over cell arrays of strings  the loop variable  let s call it f  becomes a single-element cell array  Having to write f 1  everywhere gets tedious  and modifying the loop variable provides a clean workaround     This example transposes each field of a struct  s a   1 3  s b   zeros 2 3   s   a   1 2 3   b   2x3 double  for f   fieldnames s       s  f 1     s  f 1     end s   a   3x1 double   b   3x2 double     Redefining f simplifies the indexing  for f   fieldnames s       f   f 1       s  f    s  f    end s   back to a   1 2 3   b   2x3 double

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When iterating over cell arrays of strings  the loop variable  let s call it f  becomes a single-element cell array  Having to write f 1  everywhere gets tedious  and modifying the loop variable provides a clean workaround     This example transposes each field of a struct  s a   1 3  s b   zeros 2 3   s   a   1 2 3   b   2x3 double  for f   fieldnames s       s  f 1     s  f 1     end s   a   3x1 double   b   3x2 double     Redefining f simplifies the indexing  for f   fieldnames s       f   f 1       s  f    s  f    end s   back to a   1 2 3   b   2x3 double

User · Answer

ooh  neat question   Matlab s for loop takes a matrix as input and iterates over its columns  Matlab also handles practically everything by value  no pass-by-reference  so I would expect that it takes a snapshot of the for-loop s input so it s immutable   here s an example which may help illustrate    gt  gt  A   zeros 4   A      1 16  A         1     5     9    13      2     6    10    14      3     7    11    15      4     8    12    16   gt  gt  i   1  for col   A  disp col    A   i    i  i   i   1  end       1     2     3     4       5     6     7     8       9    10    11    12      13    14    15    16   gt  gt  A  A         1     2     3     4      1     2     3     4      1     2     3     4      1     2     3     4

User · Answer

The MATLAB for loop basically allows huge flexibility  including the foreach functionality  Here some examples    1  Define start  increment and end index  for test   1 3 9    test end   2  Loop over vector  for test    1  3  4     test end   3  Loop over string  for test    hello     test end   4  Loop over a one-dimensional cell array  for test     hello   42  datestr now   1 3     test end   5  Loop over a two-dimensional cell array  for test     hello  42 datestr now     world  43 datestr now 1      test 1        test 2     disp  ---   end   6  Use fieldnames of structure arrays  s a   1 3   s b   10     for test   fieldnames s      s  cell2mat test   end

[matlab] Is there a foreach in MATLAB? If so, how does it behave if the underlying data changes?

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