Export from pig to CSV | 易学教程

问题

I'm having a lot of trouble getting data out of pig and into a CSV that I can use in Excel or SQL (or R or SPSS etc etc) without a lot of manipulation ...

I've tried using the following function:

STORE pig_object INTO '/Users/Name/Folder/pig_object.csv'
    USING CSVExcelStorage(',','NO_MULTILINE','WINDOWS');

It creates the folder with that name with lots of part-m-0000# files. I can later join them all up using cat part* > filename.csv but there's no header which means I have to put it in manually.

I've read that PigStorageSchema is supposed to create another bit with a header but it doesn't seem to work at all, eg, I get the same result as if it's just stored, no header file: STORE pig_object INTO '/Users/Name/Folder/pig_object' USING org.apache.pig.piggybank.storage.PigStorageSchema();

(I've tried this in both local and mapreduce mode).

Is there any way of getting the data out of Pig into a simple CSV file without these multiple steps?

Any help would be much appreciated!

回答1:

I'm afraid there isn't a one-liner which does the job,but you can come up with the followings (Pig v0.10.0):

A = load '/user/hadoop/csvinput/somedata.txt' using PigStorage(',') 
      as (firstname:chararray, lastname:chararray, age:int, location:chararray);
store A into '/user/hadoop/csvoutput' using PigStorage('\t','-schema');

When PigStorage takes '-schema' it will create a '.pig_schema' and a '.pig_header' in the output directory. Then you have to merge '.pig_header' with 'part-x-xxxxx' :

1. If result need to by copied to the local disk:

hadoop fs -rm /user/hadoop/csvoutput/.pig_schema
hadoop fs -getmerge /user/hadoop/csvoutput ./output.csv

(Since -getmerge takes an input directory you need to get rid of .pig_schema first)

2. Storing the result on HDFS:

hadoop fs -cat /user/hadoop/csvoutput/.pig_header 
  /user/hadoop/csvoutput/part-x-xxxxx | 
    hadoop fs -put - /user/hadoop/csvoutput/result/output.csv

For further reference you might also have a look at these posts:
STORE output to a single CSV?
How can I concatenate two files in hadoop into one using Hadoop FS shell?

回答2:

if you will store your data as PigStorage on HDFS and then merge it using -getmerge -nl:

STORE pig_object INTO '/user/hadoop/csvoutput/pig_object'
    using PigStorage('\t','-schema');
fs -getmerge -nl /user/hadoop/csvoutput/pig_object  /Users/Name/Folder/pig_object.csv;

Docs:

Optionally -nl can be set to enable adding a newline character (LF) at the end of each file.

you will have a single TSV/CSV file with the following structure:

1 - header
2 - empty line
3 - pig schema
4 - empty line
5 - 1st line of DATA
6 - 2nd line of DATA
...

so we can simply remove lines [2,3,4] using AWK:

awk 'NR==1 || NR>4 {print}' /Users/Name/Folder/pig_object.csv > /Users/Name/Folder/pig_object_clean.csv

来源：https://stackoverflow.com/questions/13696036/export-from-pig-to-csv

标签

excel

csv

apache-pig