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## 6. Structure Functions

These functions are defined in `structfuns.sl`.

## 6.1 struct_filter

Synopsis

  Apply a filter to a struct

Usage

  `struct_filter(Struct_Type s, Int_Type i)`

Description

  This function applies the filter `i` to the fields of a structure by performing the operation

  > `

  >         s.field = s.field[i];

  > `

  on each array field of the structure. Scalar fields will not be modified.

  The `dim` qualifier may be used to filter on a specific array dimension. For example, consider the structure

  > `

  >         s = struct { a = Int_Type[10], b = Int_Type[10,20] };

  > `

  Then

  > `

  >         struct_filter (s, i; dim=0);

  > `

  would produce the same result as

  > `

  >         s.a = s.a[i];
  >         s.b = s.b[i,*];

  > `

Notes

  By default this function modifies the fields of the structure passed to it. Sometimes it is desirable to create a new structure and leave the old one untouched. This may be achieved using the `copy` qualifier, e.g.,

  > `

  >          filtered_s = struct_filter (s, i; copy);

  > `

See Also

  `where`

## 6.2 struct_combine

Synopsis

  Combine two or more structures

Usage

  `new_s = struct_combine (s1, s2, ...)`

Description

  This function creates a new structure from two or more structures `s1`, `s2`,.... The new structure will have fields formed by the union of the fields of the input structures. The new structure fields will be given values that correspond to the fields of the input structures. If more than one structure has the same field name, the value of the field will be given by the last structure.

  If any of the input values is a string, or an array of strings, then it will be interpreted as a representing a structure with the corresponding field names. This is a useful feature when one wants to expand a structure with new field names, e.g.,

  > `

  >         s = struct { foo, bar };
  >         t = struct_combine (s, "baz");   % t = struct {foo, bar, baz};

  > `

See Also

  `get_struct_field_names`

## 6.3 struct_field_exists

Synopsis

  Determine whether or not a structure contains a specified field

Usage

  `Int_Type struct_field_exists (Struct_Type s, String_Type f)`

Description

  This function may be used to determine if a structure contains a field with a specfied name. It returns 0 if the structure does not contain the field, or non-zero if it does.

See Also

  `get_struct_field_names`

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