6.1.4 Manipulating Structures

Other functions that can manipulate the fields of a structure are given below.

Built-in Function: nfields (s)

Return the number of fields of the structure s.

Built-in Function: fieldnames (struct)

Return a cell array of strings naming the elements of the structure struct. It is an error to call fieldnames with an argument that is not a structure.

Built-in Function: isfield (x, name)

Return true if the x is a structure and it includes an element named name. If name is a cell array of strings then a logical array of equal dimension is returned.

Function File: [v1, …] = getfield (s, key, …)

Extract a field from a structure (or a nested structure). For example:

ss(1,2).fd(3).b = 5;
getfield (ss, {1,2}, "fd", {3}, "b")
   ⇒ 5

Note that the function call in the previous example is equivalent to the expression

i1 = {1,2}; i2 = "fd"; i3 = {3}; i4= "b";
ss(i1{:}).(i2)(i3{:}).(i4)
   ⇒ 5

See also: setfield, rmfield, isfield, isstruct, fieldnames, struct.

Function File: [k1, …, v1] = setfield (s, k1, v1, …)

Set a field member in a (nested) structure array. For example:

oo(1,1).f0 = 1;
oo = setfield (oo, {1,2}, "fd", {3}, "b", 6);
oo(1,2).fd(3).b == 6
     ⇒ ans = 1

Note that the same result as in the above example could be achieved by:

i1 = {1,2}; i2 = "fd"; i3 = {3}; i4 = "b";
oo(i1{:}).(i2)(i3{:}).(i4) == 6
     ⇒ ans = 1

See also: getfield, rmfield, isfield, isstruct, fieldnames, struct.

Built-in Function: rmfield (s, f)

Return a copy of the structure (array) s with the field f removed. If f is a cell array of strings or a character array, remove the named fields.

See also: cellstr, iscellstr, setfield.

Function File: [t, p] = orderfields (s1)

Function File: [t, p] = orderfields (s1, s2)

Return a copy of s1 with fields arranged alphabetically or as specified by s2.

Given one struct, arrange field names in s1 alphabetically.

If the second argument is a struct, arrange field names in s1 as they appear in s2. The second argument may also specify the order in a permutation vector or a cell array of strings containing the fieldnames of s1 in the desired order.

The optional second output argument p is assigned the permutation vector which converts the original name order into the new name order.

Examples:

s = struct("d", 4, "b", 2, "a", 1, "c", 3);
t1 = orderfields (s)
     ⇒ t1 =
        {
          a =  1
          b =  2
          c =  3
          d =  4
        }

t = struct("d", {}, "c", {}, "b", "a", {});
t2 = orderfields (s, t)
     ⇒ t2 =
        {
          d =  4
          c =  3
          b =  2
          a =  1
        }

t3 = orderfields (s, [3, 2, 4, 1]);
     ⇒ t3 =
        {
          a =  1
          b =  2
          c =  3
          d =  4
        }

[t4, p] = orderfields (s, {"d", "c", "b", "a"})
     ⇒ t4 =
        {
          d =  4
          c =  3
          b =  2
          a =  1
        }
        p =
           1
           4
           2
           3

See also: getfield, rmfield, isfield, isstruct, fieldnames, struct.

Function File: substruct (type, subs, …)

Create a subscript structure for use with subsref or subsasgn. For example:

idx = substruct ("()", {3, ":"})
     ⇒
       idx =
       {
         type = ()
         subs =
         {
           [1,1] =  3
           [1,2] = :
         }
       }
x = [1, 2, 3; 4, 5, 6; 7, 8, 9];
subsref (x, idx)
   ⇒ 7  8  9

See also: subsref, subsasgn.