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

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

<DL>
<DT> Synopsis <DD>
Read data from a text file
<DT> Usage <DD>
<CODE>Int_Type readascii (file, &amp;v1,...&amp;vN ; qualifiers)</CODE>
<DT> Description <DD>
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).
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.
<DT> Qualifiers <DD>
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>

<DT> Example <DD>
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.
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.
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.
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.
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>

<DT> Notes <DD>
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.
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.
<DT> See Also <DD>
<CODE>sscanf, atof, fopen, fgets, fgetslines, csv_readcol</CODE>
</DL>

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