"MR-MPI WWW Site"_mws -"MR-MPI Documentation"_md - "OINK
Documentation"_od - "OINK Commands"_oc :c

:link(mws,http://www.sandia.gov/~sjplimp/mapreduce.html)
:link(md,../doc/Manual.html)
:link(od,Manual.html)
:link(oc,Section_script.html#comm)

:line

histo command :h3

[Syntax:]

histo -i in1 -o out1.file out1.mr :pre

in1 = anthing: Key = key, Value = value
out1 = frequency count of each key: Key = key, Value = count :ul

[Examples:]

histo -i mrdata -o NULL out1.mr :pre

[Description:]

This is a named command which calculates the frequency of key occurrence
in an input set of key/values.

See the "named command"_command.html doc page for various ways in
which the -i inputs and -o outputs for a named command can be
specified.

In1 is any MR-MPI object containing key/value pairs.  The input is
unchanged by this command.

In1 cannot be specified as input from file(s) since no assumption is
made about how the files store key/value pairs.  You would need to
read the files into a MR-MPI object as a pre-processing step, using a
map() function you provide, before passing that object to the histo
command as an input.

Out1 will store the frequency count of all unique keys.

Out1 cannot be specified as output to a file since no assumption is
made about how the key should be formatted for output.  You would need
to write the files from the output MR-MPI object as a post-processing
step, using a map() or scan() function you provide.

Statistics on the count of each key will be printed to the screen in
sorted order.

[Related commands:]

"degree_stats"_degree_stats.html, "wordfreq"_wordfreq.html
