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<H1>file_sorter</H1>
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<H3>MODULE</H3>
<DIV CLASS=REFBODY>
file_sorter
</DIV>

<H3>MODULE SUMMARY</H3>
<DIV CLASS=REFBODY>
File Sorter
</DIV>

<H3>DESCRIPTION</H3>
<DIV CLASS=REFBODY>

<P>The functions of this module sort terms on files, merge already
sorted files, and check files for sortedness. Chunks containing
binary terms are read from a sequence of files, sorted
internally in memory and written on temporary files, which are
merged producing one sorted file as output. Merging is provided
as an optimization; it is faster when the files are already
sorted, but it always works to sort instead of merge.


<P>On a file, a term is represented by a header and a binary. Two
options define the format of terms on files:


<P>
<UL>

<LI>
<CODE>{header, HeaderLength}</CODE>. HeaderLength determines the
         number of bytes preceding each binary and containing the
         length of the binary in bytes. Default is 4. The order of the
         header bytes is defined as follows: if <CODE>B</CODE> is a binary
         containing a header only, the size <CODE>Size</CODE> of the binary
         is calculated as
         <CODE>&#60;&#60;Size:HeaderLength/unit:8&#62;&#62; = B</CODE>.


</LI>


<LI>
<CODE>{format, Format}</CODE>. The format determines the
function that is applied to binaries in order to create the
terms that will be sorted. The default value is
<CODE>binary_term</CODE>, which is equivalent to
<CODE>funbinary_to_term/1</CODE>. The value <CODE>binary</CODE> is
equivalent to <CODE>fun(X) -&#62; X end</CODE>, which means that the
binaries will be sorted as they are. This is the fastest
format. If <CODE>Format</CODE> is <CODE>term</CODE>, <CODE>io:read/2</CODE> is
called to read terms. In that case only the default value of
the <CODE>header</CODE> option is allowed. The <CODE>format</CODE> option
also determines what is written to the sorted output file: if
<CODE>Format</CODE> is <CODE>term</CODE> then <CODE>io:format/3</CODE> is called
to write each term, otherwise the binary prefixed by a header
is written. Note that the binary written is the same binary
that was read; the results of applying the <CODE>Format</CODE>
function are thrown away as soon as the terms have been
sorted. Reading and writing terms using the <CODE>io</CODE> module
is very much slower than reading and writing binaries.
         

</LI>


</UL>

<P>Other options are:


<P>
<UL>

<LI>
<CODE>{order, Order}</CODE>. The default is to sort terms in
         ascending order, but that can be changed by the value
         <CODE>descending</CODE> or by giving an ordering function
         <CODE>Fun</CODE>. <CODE>Fun(A,B)</CODE> should return <CODE>true</CODE>
         if <CODE>A</CODE> comes before <CODE>B</CODE> in the ordering,
         <CODE>false</CODE> otherwise. Using an ordering function will slow
         down the sort considerably. The <CODE>keysort</CODE>,
         <CODE>keymerge</CODE> and <CODE>keycheck</CODE> functions do not accept
         ordering functions.

        
</LI>


<LI>
<CODE>{unique, bool()}</CODE>. When sorting or merging files,
         only the first of a sequence of terms that compare equal is
         output if this option is set to <CODE>true</CODE>. The default
         value is <CODE>false</CODE> which implies that all terms that
         compare equal are output. When checking files for
         sortedness, a check that no pair of consecutive terms
         compares equal is done if this option is set to <CODE>true</CODE>.

        
</LI>


<LI>
<CODE>{tmpdir, TempDirectory}</CODE>. The directory where
         temporary files are put can be chosen explicitly. The
         default, implied by the value <CODE>&#34;&#34;</CODE>, is to put temporary
         files on the same directory as the sorted output file. If
         output is a function (see below), the directory returned by
         <CODE>file:get_cwd()</CODE> is used instead. The names of
         temporary files are derived from the Erlang nodename
         (<CODE>node()</CODE>), the process identifier of the current Erlang
         emulator (<CODE>os:getpid()</CODE>), and a timestamp
         (<CODE>erlang:now()</CODE>); a typical name would be
         <CODE>fs_mynode@myhost_1763_1043_337000_266005.17</CODE>, where
         <CODE>17</CODE> is a sequence number. Existing files will be
         overwritten. Temporary files are deleted unless some
         uncaught EXIT signal occurs.


</LI>


<LI>
<CODE>{compressed, bool()}</CODE>. Temporary files and the
output file may be compressed. The default value
<CODE>false</CODE> implies that written files are not
compressed. Regardless of the value of the <CODE>compressed</CODE>
option, compressed files can always be read. Note that
reading and writing compressed files is significantly slower
than reading and writing uncompressed files.

        
</LI>


<LI>
<CODE>{size, Size}</CODE>. By default approximately 512*1024
         bytes read from files are sorted internally. This option
         should rarely be needed.

        
</LI>


<LI>
<CODE>{no_files, NoFiles}</CODE>. By default 16 files are
         merged at a time. This option should rarely be needed.


</LI>


</UL>

<P>To summarize, here is the syntax of the options:

<P>
<UL>

<LI>
<CODE>Options = [Option] | Option</CODE>
        <BR>

</LI>


<LI>
<CODE>Option = {header, HeaderLength}
| {format, Format}
         | {order, Order}
         | {unique, bool()}
         | {tmpdir, TempDirectory}
         | {compressed, bool()}
| {size, Size}
         | {no_files, NoFiles}</CODE>
        <BR>

</LI>


<LI>
<CODE>HeaderLength = int() &#62; 0</CODE>
        <BR>

</LI>


<LI>
<CODE>Format = binary_term | term | binary | FormatFun</CODE>
        <BR>

</LI>


<LI>
<CODE>FormatFun = fun(Binary) -&#62; Term</CODE>
        <BR>

</LI>


<LI>
<CODE>Order = ascending | descending | OrderFun</CODE>
        <BR>

</LI>


<LI>
<CODE>OrderFun = fun(Term, Term) -&#62; bool()</CODE>
        <BR>

</LI>


<LI>
<CODE>TempDirectory = &#34;&#34; | file_name()</CODE>
        <BR>

</LI>


<LI>
<CODE>Size = int() &#62; 0</CODE>
        <BR>

</LI>


<LI>
<CODE>NoFiles = int() &#62; 1</CODE>
<BR>

</LI>


</UL>

<P>As an alternative to sorting files, a function of one argument
can be given as input. When called with the argument <CODE>read</CODE>
the function is assumed to return <CODE>end_of_input</CODE> or
<CODE>{end_of_input, Value}}</CODE> when there is no more input
(<CODE>Value</CODE> is explained below), or <CODE>{Objects, Fun}</CODE>,
where <CODE>Objects</CODE> is a list of binaries or terms depending on
the format and <CODE>Fun</CODE> is a new input function. Any other
value is immediately returned as value of the current call to
<CODE>sort</CODE> or <CODE>keysort</CODE>. Each input function will be
called exactly once, and should an error occur, the last
function is called with the argument <CODE>close</CODE>, the reply of
which is ignored.


<P>A function of one argument can be given as output. The results
of sorting or merging the input is collected in a non-empty
sequence of variable length lists of binaries or terms depending
on the format. The output function is called with one list at a
time, and is assumed to return a new output function. Any other
return value is immediately returned as value of the current
call to the sort or merge function. Each output function is
called exactly once. When some output function has been applied
to all of the results or an error occurs, the last function is
called with the argument <CODE>close</CODE>, and the reply is returned
as value of the current call to the sort or merge function. If a
function is given as input and the last input function returns
<CODE>{end_of_input, Value}</CODE>, the function given as output will
be called with the argument <CODE>{value, Value}</CODE>. This makes it
easy to initiate the sequence of output functions with a value
calculated by the input functions.


<P>As an example, consider sorting the terms on a disk log file.
A function that reads chunks from the disk log and returns a
list of binaries is used as input. The results are collected in
a list of terms.

<PRE>
sort(Log) -&#62;
    {ok, _} = disk_log:open([{name,Log}, {mode,read_only}]),
    Input = input(Log, start),
    Output = output([]),
    Reply = file_sorter:sort(Input, Output, {format,term}),
    ok = disk_log:close(Log),
    Reply.

input(Log, Cont) -&#62;
    fun(close) -&#62;
            ok;
       (read) -&#62;
            case disk_log:chunk(Log, Cont) of
                {error, Reason} -&#62;
                    {error, Reason};
                {Cont2, Terms} -&#62;
                    {Terms, input(Log, Cont2)};
                {Cont2, Terms, _Badbytes} -&#62;
                    {Terms, input(Log, Cont2)};
                eof -&#62;
                    end_of_input
            end
    end.

output(L) -&#62;
    fun(close) -&#62;
            lists:append(lists:reverse(L));
       (Terms) -&#62;
            output([Terms | L])
    end.
</PRE>

<P>Further examples of functions as input and output can be found
at the end of the <CODE>file_sorter</CODE> module; the <CODE>term</CODE>
format is implemented with functions.


<P>The possible values of <CODE>Reason</CODE> returned when an error
occurs are:

<P>
<UL>

<LI>
<CODE>bad_object</CODE>, <CODE>{bad_object, FileName}</CODE>. 
         Applying the format function failed for some binary, 
         or the key(s) could not be extracted from some term.
         <BR>

</LI>


<LI>
<CODE>{bad_term, FileName}</CODE>. <CODE>io:read/2</CODE> failed
         to read some term.      
         <BR>

</LI>


<LI>
<CODE>{file_error, FileName, Reason2}</CODE>. See
         <CODE>file(3)</CODE> for an explanation of <CODE>Reason2</CODE>.
         <BR>

</LI>


<LI>
<CODE>{premature_eof, FileName}</CODE>. End-of-file was 
         encountered inside some binary term.
         <BR>

</LI>


<LI>
<CODE>{not_a_directory, FileName}</CODE>. The file
         supplied with the <CODE>tmpdir</CODE> option is not a directory.
<BR>

</LI>


</UL>

<P><STRONG>Types</STRONG>

<PRE>
Binary = binary()
FileName = file_name()
FileNames = [FileName]
ICommand = read | close
IReply = end_of_input | {end_of_input, Value} | {[Object], Infun} | InputReply
Infun = fun(ICommand) -&#62; IReply
Input = FileNames | Infun
InputReply = Term
KeyPos = int() &#62; 0 | [int() &#62; 0]
OCommand = {value, Value} | [Object] | close
OReply = Outfun | OutputReply
Object = Term | Binary
Outfun = fun(OCommand) -&#62; OReply
Output = FileName | Outfun
OutputReply = Term
Term = term()
Value = Term
    
</PRE>

</DIV>

<H3>EXPORTS</H3>

<P><A NAME="sort/1"><STRONG><CODE>sort(FileName) -&#62; Reply</CODE></STRONG></A><BR>
<A NAME="sort/2"><STRONG><CODE>sort(Input, Output) -&#62; Reply</CODE></STRONG></A><BR>
<A NAME="sort/3"><STRONG><CODE>sort(Input, Output, Options) -&#62; Reply</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Reply = ok | {error, Reason} | InputReply | OutputReply</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Sorts terms on files. 


<P><CODE>sort(FileName)</CODE> is equivalent to
         <CODE>sort([FileName], FileName)</CODE>.

         
<P><CODE>sort(Input, Output)</CODE> is equivalent to
         <CODE>sort(Input, Output, [])</CODE>.

         
<P> 
</DIV>

<P><A NAME="keysort/2"><STRONG><CODE>keysort(KeyPos, FileName) -&#62; Reply</CODE></STRONG></A><BR>
<A NAME="keysort/3"><STRONG><CODE>keysort(KeyPos, Input, Output) -&#62; Reply</CODE></STRONG></A><BR>
<A NAME="keysort/4"><STRONG><CODE>keysort(KeyPos, Input, Output, Options) -&#62; Reply</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Reply = ok | {error, Reason} | InputReply | OutputReply</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Sorts tuples on files. The sort is performed on the
element(s) mentioned in <CODE>KeyPos</CODE>. If two tuples
compare equal on one element, next element according to
<CODE>KeyPos</CODE> is compared. The sort is stable.


<P><CODE>keysort(N, FileName)</CODE> is equivalent to
         <CODE>keysort(N, [FileName], FileName)</CODE>.

         
<P><CODE>keysort(N, Input, Output)</CODE> is equivalent to
         <CODE>keysort(N, Input, Output, [])</CODE>.

         
<P> 
</DIV>

<P><A NAME="merge/2"><STRONG><CODE>merge(FileNames, Output) -&#62; Reply</CODE></STRONG></A><BR>
<A NAME="merge/3"><STRONG><CODE>merge(FileNames, Output, Options) -&#62; Reply</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Reply = ok | {error, Reason} | OutputReply</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Merges terms on files. Each input file is assumed to be
sorted.


<P><CODE>merge(FileNames, Output)</CODE> is equivalent to
         <CODE>merge(FileNames, Output, [])</CODE>.


</DIV>

<P><A NAME="keymerge/3"><STRONG><CODE>keymerge(KeyPos, FileNames, Output) -&#62; Reply</CODE></STRONG></A><BR>
<A NAME="keymerge/4"><STRONG><CODE>keymerge(KeyPos, FileNames, Output, Options) -&#62; Reply</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Reply = ok | {error, Reason} | OutputReply</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Merges tuples on files. Each input file is assumed to be
sorted on key(s).


<P><CODE>keymerge(KeyPos, FileNames, Output)</CODE> is equivalent
         to <CODE>keymerge(KeyPos, FileNames, Output, [])</CODE>.

         
<P> 
</DIV>

<P><A NAME="check/1"><STRONG><CODE>check(FileName) -&#62; Reply</CODE></STRONG></A><BR>
<A NAME="check/2"><STRONG><CODE>check(FileNames, Options) -&#62; Reply</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Reply = {ok, [Result]} | {error, Reason}</CODE></STRONG><BR>
<STRONG><CODE>Result = {FileName, TermPosition, Term}</CODE></STRONG><BR>
<STRONG><CODE>TermPosition = int() &#62; 1</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Checks files for sortedness. If a file is not sorted, the
         first out-of-order element is returned. The first term on a
         file has position 1.


<P><CODE>check(FileName)</CODE> is equivalent to
         <CODE>check([FileName], [])</CODE>.


</DIV>

<P><A NAME="keycheck/2"><STRONG><CODE>keycheck(KeyPos, FileName) -&#62; CheckReply</CODE></STRONG></A><BR>
<A NAME="keycheck/3"><STRONG><CODE>keycheck(KeyPos, FileNames, Options) -&#62; Reply</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Reply = {ok, [Result]} | {error, Reason}</CODE></STRONG><BR>
<STRONG><CODE>Result = {FileName, TermPosition, Term}</CODE></STRONG><BR>
<STRONG><CODE>TermPosition = int() &#62; 1</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Checks files for sortedness. If a file is not sorted, the
         first out-of-order element is returned. The first term on a
         file has position 1.


<P><CODE>keycheck(KeyPos, FileName)</CODE> is equivalent
         to <CODE>keycheck(KeyPos, [FileName], [])</CODE>.

         
<P> 
</DIV>

<H3>AUTHORS</H3>
<DIV CLASS=REFBODY>
Hans Bolinder - support@erlang.ericsson.se<BR>

</DIV>
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<SMALL>stdlib 1.14.2<BR>
Copyright &copy; 1991-2006
<A HREF="http://www.erlang.se">Ericsson AB</A><BR>
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