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Split CSV by column value, and keep header

This has been asked many times before but I simply can't implement the solutions properly. I have a large csv named 2017-01.csv, with a date column (it's the second column in the file) and I am splitting the file by date. The original file looks like:

date
2017-01-01
2017-01-01
2017-01-01
2017-01-02
2017-01-02
2017-01-02


After the split, 2017-01-01.csv looks like

2017-01-01
2017-01-01
2017-01-01


and 2017-01-02.csv looks like

2017-01-02
2017-01-02
2017-01-02


The code I am using is

awk -F ',' '{print > (""$2".csv")}' 2017.csv


Everything works fine but I need to keep the header row. So I tried

awk -F ',' 'NR==1; NR > 1{print > (""$2".csv")}' 2017-01.csv


But I still get the same results without the header row. What am I doing wrong? I read answers to many similar questions on Stackoverflow but I just can't understand what they are doing.

I want this:

2017-01-01.csv should look like

date
2017-01-01
2017-01-01
2017-01-01


2017-01-02.csv should look like

date
2017-01-02
2017-01-02
2017-01-02


1 Answer
1

Could you please try following, I haven't tested it though. Considering that your Input_file is in sorted order.

awk 'prev!=$0{close(file);file=$0".csv";print "date" > file} {print > file;prev=$0}' 2017-01.csv


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