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https://issues.apache.org/jira/browse/MADLIB-1240?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16489677#comment-16489677
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Frank McQuillan commented on MADLIB-1240:
-----------------------------------------
Is that something that we can easily and reliably trap apriori?
https://www.postgresql.org/docs/10/static/ddl-basics.html
“There is a limit on how many columns a table can contain. Depending on the
column types, it is between 250 and 1600.”
We need to consider both the feature vector to be "columnized" and the
'cols_to_output' parameter in this module, since both contribute to the number
of columns and column types. Maybe it is better to just let Postgres/Greenplum
throw an error if it is too big? What is the value of trying to trap?
> Vector to Columns
> -----------------
>
> Key: MADLIB-1240
> URL: https://issues.apache.org/jira/browse/MADLIB-1240
> Project: Apache MADlib
> Issue Type: New Feature
> Components: Module: Utilities
> Reporter: Frank McQuillan
> Priority: Major
> Fix For: v1.15
>
>
> related to https://issues.apache.org/jira/browse/MADLIB-1239
> Vector to Columns
> Converts a feature array in a single column of an output table into multiple
> columns. This process can be used to reverse the function cols2vec.
> {code}
> vec2cols(
> source_table,
> out_table,
> vector_col,
> dictionary,
> 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.
> vector_col
> TEXT. Name of the column containing the feature array. Must be a
> one-dimensional array.
> dictionary (optional)
> TEXT. Name of the table containing the array of names associated with the
> feature array. This table is created by the function 'cols2vec'. If the
> dictionary table is not specified, column names will be automatically
> generated of the form 'feature_1, feature_2, ...feature_n'
> 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 columns. To
> keep all columns from the source table, use '*'.
> Output
> The output table produced by the vec2cols function contains the following
> columns:
> <...>
> Columns from source table, depending on which ones are kept (if any).
> feature columns
> Columns for each of the features in 'vector_col'. Column type will depend on
> the feature array type in the source table. Column naming will depend on
> whether the parameter 'dictionary' is used.
> {code}
> Notes
> (1)
> The function
> http://pivotalsoftware.github.io/PDLTools/group__ArrayUtilities.html
> 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}
> vec2cols(
> table_name,
> output_table,
> vector_column,
> NULL,
> '*'
> )
> {code}
> (2)
> Please put the generated feature columns on the right side of the output
> table, i.e., they will be the last column on the right. Maintain the order
> of the array.
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