Controlling VW's output

VW can produce several logical streams of output:

• Driver
• Logging
• Audit
• Predictions

Driver

This describes the run. Configuration, progressive results and then final results.

This can be turned off with --driver_output_off, or with --quiet. By default, this goes to stderr but --driver_output_stream [stdout|stderr] can be used to select stdout or stderr.

Example

only testing
predictions = 0001.predict
Num weight bits = 18
learning rate = 10
initial_t = 1
power_t = 0.5
using no cache
Reading datafile = train-sets/0001.dat
num sources = 1
Enabled reductions: gd, scorer-identity, count_label
Input label = simple
Output pred = scalar
average  since         example        example  current  current  current
loss     last          counter         weight    label  predict features
0.000000 0.000000            1            1.0   1.0000   1.0000      290
0.000000 0.000000            2            2.0   0.0000   0.0000      608
0.000000 0.000000            4            4.0   0.0000   0.0000      794
0.000000 0.000000            8            8.0   0.0000   0.0000      860
0.000000 0.000000           16           16.0   1.0000   1.0000      128
0.000000 0.000000           32           32.0   0.0000   0.0000      176
0.000000 0.000000           64           64.0   0.0000   0.0000      350
0.000000 0.000000          128          128.0   1.0000   1.0000      620

finished run
number of examples = 200
weighted example sum = 200.000000
weighted label sum = 91.000000
average loss = 0.000000
best constant = 0.455000
best constant's loss = 0.247975
total feature number = 89692

Logging

VW produces log messages during operation. --log_level [info|warning|error|critical|off] can be used to filter which levels to show. --quiet implies --log_level off and takes higher priority.

The destination stream can be selected with --log_output_stream [stdout|stderr|compat]. In the past, VW produced log like messages to a mix of both stdout and stderr, compat maintains this old behavior is the current default. stdout or stderr should be chosen as compat will be removed at some point.

These messages always start with [warning] and can span multiple lines.

If there are many messages being produced --limit_output <num_messages> can be used to limit the number of log messages produced.

Example

[warning] NAN prediction in example 1, forcing 0

Audit

A description of audit can be found here. These messages currently only go to stdout.

Predictions

Predictions which VW produces can be output with --predictions <output_file>. If stdout is passed, the results will be printed to stdout, otherwise they are written to a file with that name.