Frank McQuillan created MADLIB-1239:
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Summary: Columns to Vector
Key: MADLIB-1239
URL: https://issues.apache.org/jira/browse/MADLIB-1239
Project: Apache MADlib
Issue Type: New Feature
Components: Module: Utilities
Reporter: Frank McQuillan
Fix For: v1.15
Columns to Vector
Converts features from multiple columns of an input table into a feature array
in a single column. Also outputs the names of the features into an array in a
single column. This process can be reversed using the function vec2cols.
{code}
cols2vec(
source_table,
out_table,
list_of_features,
list_of_features_to_exclude,
cols_to_output
)
source_table
TEXT. Name of the table containing the source data.
out_table
TEXT. Name of the generated table containing the output. If a table with the
same name already exists, an error will be returned.
list_of_features
TEXT. Comma-separated string of column names or expressions to put into array.
Can also be a '*' implying all columns are to be put into array (except for the
ones included in the next argument that lists exclusions). The types of the
features should all be the same since PostgreSQL arrays only support elements
of the same type. If multiple numeric types are present in the source table,
they will be cast to DOUBLE PRECISION.
Array columns can also be included in the list, and the array will be expanded
to treat each element of the array as a separate feature.
list_of_features_to_exclude (optional)
TEXT, default NULL. Comma-separated string of column names to exclude from the
feature array. Use only when list_of_features is '*'.
cols_to_output (optional)
TEXT, default NULL. Comma-separated string of column names from the source
table to keep in the output table, in addition to the feature array. To keep
all columns from the source table, use '*'.
Output
The output table produced by the cols2vec function contains the following
columns:
<...>
Columns from source table, depending on which ones are kept (if any).
feature_vector
Array of features. Array type will depend on feature type in the source table.
feature_names
TEXT[] Array of names of features.
{code}
Open questions for cols2vec:
1) OK to cast to double if there are mixed numeric types? Or should we enforce
that all feature columns be the exact same type? (Since elements of PostgreSQL
arrays need to be the same type.)
Aside
The function
http://pivotalsoftware.github.io/PDLTools/group__grp__array__utilities.html#cols2vec_example
is similar but the proposed MADlib one has more options. To do the equivalent
of the PDL Tools one in MADlib, you would do:
{code}
cols2vec(
table_name,
output_table,
'*',
exclude_columns
)
{code}
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