--add_ngrams

Switch

--add_ngrams [-n N [N2...] ]

Description

Extract ngrams (words and phrases) from a message table

Argument and Default Value

by default (i.e. if -n isn’t present), N is set to 1.

Details

This switch tokenizes the given message table into N-grams and then aggregates them over each group_id. A n-gram is either a single word or token (n=1; e.g. “hello”, “:)”, “youtube.com”) or a phrase (n>1; e.g. “happy birthday”, “changes saved”). Once all of a group’s messages are split into n-grams , the n-grams are counted (i.e. summed) (both raw count and relative frequency over that group_id) and inserted into a feature table that will be named something like “feat$ngram$message_table$group_id$16to16” (where the italicized items are determined by your command setup) Note that the n-grams are all lowercased.

By default spaces are shrunk and newlines ('n') are replaced by '<newline>'.

The feature table will have the following columns (at least):

• group_id whatever values that the message table has in the -g column (is an index)

• feat ngrams (utf8mb4 encoded usually; also an index)

• value raw count of how many times the ngram appears in the group

• group_norm normalized frequency of ngram in group

Other Switches

Required Switches:

• -d, -g, -t

Optional Switches:

• --anscombe, --sqrt, --log, --boolean

• --combine_feat_tables

• --feat_occ_filter

• --feat_colloc_filter

• --no_metafeats

Example Commands

Creates 1gram features and save in feat$1gram$msgs$user_id$16to16.

dlatkInterface.py -d dla_tutorial -t msgs -c user_id --add_ngrams

This command will create tables for 1grams (feat$1gram$msgs$user_id$16to16) and 2grams (feat$2gram$msgs$user_id$16to16) and then a third table which contains 1-2grams (feat$1to2gram$msgs$user_id$16to16).

dlatkInterface.py -d dla_tutorial -t msgs -c user_id --add_ngrams -n 1 2 --combine_feat_tables 1to2gram