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https://issues.apache.org/jira/browse/MADLIB-1239?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16498641#comment-16498641
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Frank McQuillan commented on MADLIB-1239:
-----------------------------------------
[~hpandey]
(1)
If cols_to_output = NULL (default), it means to only output the feature vector,
and no other columns from the source_table. If the user wants out_table
contain all the source table columns + feature vector, they should specify '*'
for the parameter cols_to_output. If they only want columns 'a' and 'b' to be
output along with the feature vector, they would say cols_to_output = 'a, b'
See sessionize for an example
http://madlib.apache.org/docs/latest/group__grp__sessionize.html
(2)
The parameter list_of_features_to_exclude only makes sense when
list_of_features = '*'.
For example if you say:
list_of_features = '*'
list_of_features_to_exclude = 'x, y, z'
it means use all of the columns from the source table for features, except for
x, y, z
See decision tree for an example
http://madlib.apache.org/docs/latest/group__grp__decision__tree.html
Also, please ensure that you handle special characters and UTF-8 in the usual
way.
Also, please ensure to maintain column order.
> 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
> Assignee: Himanshu Pandey
> Priority: Major
> Fix For: v1.15
>
>
> related to https://issues.apache.org/jira/browse/MADLIB-1240
> Columns to Vector
> Converts features from multiple columns of an input table into a feature
> 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
> feature array. Can also be a '*' implying all columns are to be put into
> feature array (except for the ones included in the next argument that lists
> exclusions). Array columns in the source table are not supported in the
> 'list_of_features'.
> PostgreSQL arrays only allow elements of the same type. If multiple numeric
> types are present in the 'list_of_features', they will be cast to the largest
> type. For example, if there are INTEGER and DOUBLE PRECISION columns in the
> feature list, the feature array will be of type DOUBLE PRECISION[]. Invalid
> combinations like TEXT and INTEGER will result in an error.
> 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.
> A summary table named <out_table>_summary is also created at the same time,
> which lists the names of the features.
> feature_names
> TEXT[] Array of names of features.
> {code}
> Notes
> (1)
> 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}
> (2)
> Please put the feature vector on the right side of the output table, i.e., it
> will be the last column on the right.
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