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From "Lance Norskog (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-2208) Flexible CSV text parser InputFormat
Date Fri, 22 Jul 2011 08:57:58 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-2208?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13069451#comment-13069451
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Lance Norskog commented on MAPREDUCE-2208:
------------------------------------------

Hadoop assumes that it will process several files of the same format. Will every CSV file
have the same header? If you split a giant CSV file into many pieces, will you reproduce the
header line on the 2nd through N file?

Hadoop jobs are generally configured with total knowledge of the data. The mappers are hard-coded
for the input formats.

The code could include a rule for how to decide that the first line is a header and skip over
it. That would be worth adding.

> Flexible CSV text parser InputFormat
> ------------------------------------
>
>                 Key: MAPREDUCE-2208
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-2208
>             Project: Hadoop Map/Reduce
>          Issue Type: New Feature
>            Reporter: Lance Norskog
>            Priority: Trivial
>         Attachments: CSVTextInputFormat.java, TestCSVTextFormat.java
>
>
> CSVTextInputFormat is a configurable CSV parser tuned to most of the csv-style datasets
I've found. The Hadoop samples I've seen all FileInputFormat and Mapper<LongWritable,Text>.
They drop the Longwritable key and parse the Text value as a CSV line. But, they are all custom-coded
for the format.
> CSVTextInputFormat takes any csv-encoded file and rearrange the fields into the format
required by a Mapper. You can drop fields & rearrange them. There is also a random sampling
option to make training/test runs easier.
> Attached are CSVTextInputFormat.java and a unit test for it. Both go into org.apache.hadoop.mapreduce.lib.input
under src/java and test/mapred/src.
> This is compiled against hadoop-0.0.20.

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