Ruby - Delete rows in csv file using enumerator CSV.open - ruby

Question

I know how to do it with CSV.read, but CSV.open and enumerator I'm not sure how. Or how do I omit those specific row before loading them in the new_csv[] ?
Thanks!
new_csv = []
CSV.open(file, headers:true) do |unit|
units = unit.each
units.select do |row|
#delete row [0][1][2][3]
new_csv << row
end
Code Example

Answer 1

If you want to skip the first four rows plus the header, this are some options.
Get pure array:
new_csv = CSV.read(filename)[5..]
or keep the csv object
new_csv = []
CSV.open(filename, headers:true) do |csv|
csv.each_with_index do |row, i|
new_csv << row if i > 3
end
end
or using Enumerable#each_with_object:
csv = CSV.open(filename, headers:true)
new_csv = csv.each_with_index.with_object([]) do |(row, i), ary|
ary << row if i > 3
end

Answer 2

Let's begin by creating a CSV file:
contents =<<~END
name,nickname,age
Robert,Bobbie,23
Wilma,Stretch,45
William,Billy-Bob,72
Henrietta,Mama,53
END
FName = 'x.csv'
File.write(FName, contents)
#=> 91
We can use CSV::foreach without a block to return an enumerator.
csv = CSV.foreach(FName, headers:true)
#=> #<Enumerator: CSV:foreach("x.csv", "r", headers: true)>
The enumerator csv generates CSV::ROW objects:
obj = csv.next
#=> #<CSV::Row "name":"Robert" "nickname":"Bobbie" "age":"23">
obj.class
#=> CSV::Row
Before continuing let me Enumerator#rewind csv so that csv.next will once again generate its first element.
csv.rewind
Suppose we wish to skip the first two records. We can do that using Enumerator#next:
2.times { csv.next }
Now continue generating elements with the enumerator, mapping them to an array of hashes:
loop.map { csv.next.to_h }
#=> [{"name"=>"William", "nickname"=>"Billy-Bob", "age"=>"72"},
# {"name"=>"Henrietta", "nickname"=>"Mama", "age"=>"53"}]
See Kernel#loop and CSV::Row#to_h. The enumerator csv raises a StopInteration exception when next invoked after the enumerator has generated its last element. As you see from its doc, loop handles that exception by breaking out of the loop.
loop is a very versatile method. I generally use it in place of while and until, as well as when I need it to handle a StopIteration exception.
If you just want the values, then:
csv.rewind
2.times { csv.next }
loop.with_object([]) { |_,arr| arr << csv.next.map(&:last) }
#=> [["William", "Billy-Bob", "72"],
# ["Henrietta", "Mama", "53"]]