how to read first 5 lines of csv file using built in ruby csv

Question

My application lets user to upload csv file with maximum of 50MB. I wanted to show the user the preview of the uploaded file. Can I read only the first 5 lines of csv? I am currently using CSV.read function, obviously this will read the entire file and is slow.

This should help you: stackoverflow.com/questions/10236328/… — Jens
– Jens, Commented Sep 7, 2018 at 5:42

Aleksei Matiushkin · Accepted Answer · 2018-09-07 07:05:49Z

17

CSV#foreach returns an enumerable, so just call Enumerable#take on it:

csv_preview_data = CSV.foreach(csv_path, headers: false).take(5)

answered Sep 7, 2018 at 7:05

Aleksei Matiushkin

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2 Comments

Roman Kiselenko Over a year ago

Does it reads only first 5 lines without loading all file in the memory?

Aleksei Matiushkin Over a year ago

@Зелёный foreach.lazy.take(5).force probably does is lazily.

John Baker · Accepted Answer · 2018-09-07 09:29:08Z

1

The simplest ways to read a fixed number of records for my opinion would be:

preview_data = CSV.readlines(csv_path, headers: false)[0,5]

answered Sep 7, 2018 at 9:29

John Baker

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1 Comment

Edgar Ortega Over a year ago

This will load the entire CSV into memory, avoid this method for big files

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