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<H2><A NAME="s6">6.</A> <A HREF="slshfun.html#toc6">Structure Functions</A></H2>

<P>These functions are defined in <CODE>structfuns.sl</CODE>.</P>
<H2><A NAME="struct_filter"></A> <A NAME="ss6.1">6.1</A> <A HREF="slshfun.html#toc6.1"><B>struct_filter</B></A>
</H2>

<P>
<DL>
<DT><B> Synopsis </B><DD>
<P>Apply a filter to a struct</P>
<DT><B> Usage </B><DD>
<P><CODE>struct_filter(Struct_Type s, Int_Type i)</CODE></P>
<DT><B> Description </B><DD>
<P>This function applies the filter <CODE>i</CODE> to the fields of a structure
by performing the operation
<BLOCKQUOTE><CODE>
<PRE>
    s.field = s.field[i];
</PRE>
</CODE></BLOCKQUOTE>

on each array field of the structure.  Scalar fields will not be modified.</P>
<P>The <CODE>dim</CODE> qualifier may be used to filter on a specific array
dimension.  For example, consider the structure
<BLOCKQUOTE><CODE>
<PRE>
    s = struct { a = Int_Type[10], b = Int_Type[10,20] };
</PRE>
</CODE></BLOCKQUOTE>

Then 
<BLOCKQUOTE><CODE>
<PRE>
    struct_filter (s, i; dim=0);
</PRE>
</CODE></BLOCKQUOTE>

would produce the same result as
<BLOCKQUOTE><CODE>
<PRE>
    s.a = s.a[i];
    s.b = s.b[i,*];
</PRE>
</CODE></BLOCKQUOTE>
</P>
<DT><B> Notes </B><DD>
<P>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
<CODE>copy</CODE> qualifier, e.g.,
<BLOCKQUOTE><CODE>
<PRE>
     filtered_s = struct_filter (s, i; copy);
</PRE>
</CODE></BLOCKQUOTE>
</P>
<DT><B> See Also </B><DD>
<P><CODE>where</CODE></P>
</DL>
</P>


<H2><A NAME="struct_combine"></A> <A NAME="ss6.2">6.2</A> <A HREF="slshfun.html#toc6.2"><B>struct_combine</B></A>
</H2>

<P>
<DL>
<DT><B> Synopsis </B><DD>
<P>Combine two or more structures</P>
<DT><B> Usage </B><DD>
<P><CODE>new_s = struct_combine (s1, s2, ...)</CODE></P>
<DT><B> Description </B><DD>
<P>This function creates a new structure from two or more structures
<CODE>s1</CODE>, <CODE>s2</CODE>,....  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.</P>
<P>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.,
<BLOCKQUOTE><CODE>
<PRE>
    s = struct { foo, bar };
    t = struct_combine (s, "baz");   % t = struct {foo, bar, baz};
</PRE>
</CODE></BLOCKQUOTE>
</P>
<DT><B> See Also </B><DD>
<P><CODE>get_struct_field_names</CODE></P>
</DL>
</P>


<H2><A NAME="struct_field_exists"></A> <A NAME="ss6.3">6.3</A> <A HREF="slshfun.html#toc6.3"><B>struct_field_exists</B></A>
</H2>

<P>
<DL>
<DT><B> Synopsis </B><DD>
<P>Determine whether or not a structure contains a specified field</P>
<DT><B> Usage </B><DD>
<P><CODE>Int_Type struct_field_exists (Struct_Type s, String_Type f)</CODE></P>
<DT><B> Description </B><DD>
<P>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.</P>
<DT><B> See Also </B><DD>
<P><CODE>get_struct_field_names</CODE></P>
</DL>
</P>


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