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<H2><A NAME="s5">5.</A> <A HREF="slshfun.html#toc5">Reading Text-formated Data Files</A></H2>

<P>These functions are defined in <CODE>readascii.sl</CODE>.  For comma or
tab-delimited files, consider useing the CSV module.</P>
<H2><A NAME="readascii"></A> <A NAME="ss5.1">5.1</A> <A HREF="slshfun.html#toc5.1"><B>readascii</B></A>
</H2>

<P>
<DL>
<DT><B> Synopsis </B><DD>
<P>Read data from a text file</P>
<DT><B> Usage </B><DD>
<P><CODE>Int_Type readascii (file, &amp;v1,...&amp;vN ; qualifiers)</CODE></P>
<DT><B> Description </B><DD>
<P>This function may be used to read formatted data from a text (as
opposed to binary) file and stores the values as arrays in the
specified variables <CODE>v1,..., vN</CODE> (passed as references).  It
returns the number of lines read from the file that matched the
format (implicit or specified by a qualifier).</P>
<P>The file parameter may be a string that gives the filename to read,
a <CODE>File_Type</CODE> object representing an open file pointer, or an
array of lines to be scanned.</P>
<DT><B> Qualifiers </B><DD>
<P>The following qualifiers are supported by the function
<BLOCKQUOTE><CODE>
<PRE>
   format=string        The sscanf format string to be used when
                          parsing lines.
   nrows=integer        The maximum number of matching rows to handle.
   ncols=integer        If a single reference is passed, it will be
                          assigned an array of ncols arrays of data values.
   skip=integer         Skip the specified number of lines before
                          scanning
   maxlines=integer     Read no more than this many lines.
   cols=Array_Type      Read only the specified (1-based) columns.
                          Used with an implict format
   delim=string         For an implicit format, use this as a field
                          separator.  The default is whitespace.
   type=string          For an implicit format, use this sscanf type
                          specifier.  Default is %lf (Double_Type).
   size=integer         Use this value as the initial size for the
                          arrays.
   dsize=integer        Use this value as an increment when
                          reallocating the arrays.
   stop_on_mismatch     Stop reading input when a line does not match
                          the format
   lastline=&amp;v          Assign the last line read to the variable v.
   lastlinenum=&amp;v       Assign the last line number (1-based to v)
   comment=string       Lines beginning with this string are ignored.
   as_list              If present, then return data in lists rather
                          than arrays.
</PRE>
</CODE></BLOCKQUOTE>
</P>
<DT><B> Example </B><DD>
<P>As a simple example, consider a file called <CODE>imped.dat</CODE> containing
<BLOCKQUOTE><CODE>
<PRE>
    # Distance    Zr   Zi
    0.0          50.2    0.1
    1.0          47.3  -12.2
    2.0          43.9  -15.8
</PRE>
</CODE></BLOCKQUOTE>

The 3 columns may be read and stored in the variables <CODE>x</CODE>, <CODE>zr</CODE>,
<CODE>zi</CODE> using
<BLOCKQUOTE><CODE>
<PRE>
     n = readascii ("imped.dat", &amp;x, &amp;zr, &amp;zi);
</PRE>
</CODE></BLOCKQUOTE>

After return, The value of <CODE>x</CODE> will be set to
<CODE>[0.0,1.0,2.0]</CODE>, <CODE>zr</CODE> to <CODE>[50.2,47.3,43.9]</CODE>,
<CODE>zi</CODE> to <CODE>[0.1,-12.2,-15.8]</CODE>, and <CODE>n</CODE> to 3.</P>
<P>Another way to read the same data is to use
<BLOCKQUOTE><CODE>
<PRE>
    n = readascii ("imped.dat", &amp;data; ncols=3);
</PRE>
</CODE></BLOCKQUOTE>

In this case, <CODE>data</CODE> will be <CODE>Array_Type[3]</CODE>, with each
element of the array containing the array of data values for the
corresponding column.  As before, <CODE>n</CODE> will be 3.</P>
<P>As a more complex example, Consider a file called <CODE>score.dat</CODE>
that contains:
<BLOCKQUOTE><CODE>
<PRE>
    Name      Score     Date          Flags
    Bill       73.2     03-Nov-2046    1
    James      22.9     03-Nov-2046    1
    Lucy       89.1     04-Nov-2046    3
</PRE>
</CODE></BLOCKQUOTE>

This file may be read using
<BLOCKQUOTE><CODE>
<PRE>
     n = readascii ("score.dat", &amp;name, &amp;score, &amp;date, &amp;flags;
                    format="%s %lf %s %d");
</PRE>
</CODE></BLOCKQUOTE>

In this case, <CODE>n</CODE> will be 3, <CODE>name</CODE> and <CODE>date</CODE> will
be <CODE>String_Type</CODE> arrays, <CODE>score</CODE> will be a
<CODE>Double_Type</CODE> array, and <CODE>flags</CODE> will be an
<CODE>Int_Type</CODE> array.</P>
<P>Now suppose that only the score and flags column are of interest.
The <CODE>name</CODE> and <CODE>date</CODE> fields may be ignored using
<BLOCKQUOTE><CODE>
<PRE>
     n = readascii ("score.dat", &amp;score, &amp;flags";
                    format="%*s %lf %*s %d");
</PRE>
</CODE></BLOCKQUOTE>

Here, <CODE>%*s</CODE> indicates that the field is to be parsed as a
string, but not assigned to a variable.</P>
<P>Consider the task of reading columns from a file called
<CODE>books.dat</CODE> that contain quoted strings such as:
<BLOCKQUOTE><CODE>
<PRE>
     # Year  Author Title
     "1605" "Miguel de Cervantes"  "Don Quixote de la Mancha"
     "1885" "Mark Twain" "The Adventures of Huckleberry Finn"
     "1955" "Vladimir Nabokov" "Lolita"
</PRE>
</CODE></BLOCKQUOTE>

Such a file may be read using
<BLOCKQUOTE><CODE>
<PRE>
     n = readascii ("books.dat", &amp;year, &amp;author, &amp;title;
                    format="\"%[^\"]\" \"%[^\"]\" \"%[^\"]\"");
</PRE>
</CODE></BLOCKQUOTE>
</P>
<DT><B> Notes </B><DD>
<P>This current version of this function does not handle missing data.
For such files, the <CODE>csv_readcol</CODE> function might be a better
choice.</P>
<P>By default, lines not matching the expected format are assumed to
be comments and are skipped.  So normally the <CODE>comment</CODE>
qualifier is not needed.  However, it is useful in conjunction with
the <CODE>stop_on_mismatch</CODE> qualifier to force the parser to skip
lines beginning with the comment string and continue scanning.</P>
<DT><B> See Also </B><DD>
<P><CODE>sscanf, atof, fopen, fgets, fgetslines, csv_readcol</CODE></P>
</DL>
</P>


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