How to remove lines where the first "word" is non-unique

Question

I have a large data file of comma separated variables. I need to remove all lines where the first entry (a number up to four digits) is non-unique. A typical example of what I am working with is below

1062,"Mark","Michaelson","1"
1062,"Mark","Michaelson","2"
1062,"Mark","Michaelson","4120"
1075,"Dan","Danson",15"
1075,"Dan","Danson",185"

so in the brief example above, I wish to retain the first and forth lines and discard the rest.

I have been trying to use Vim Regex to achieve this

:0/^\w*/+,$g//d

but of course that deletes all lines apart from the first

Answer 1

The g/ only solution would probably be

:g/^\(\d\{4}\).\+\n\_.*\%(^\1\D\)/d

This leaves the last occurrence. We look for lines which have another line starting with the same digits an arbitrary number of characters ahead. The key is the \_.* in the middle which subsumes as much as possible.

The equivalent very magic version is

:g/\v^(\d{4}).+\n\_.*%(^\1\D)/d

Another solution is to use :s and the sub-replace-expression \=,

let seen = {} | %s/^\(\d\{4}\).\+\n/\= has_key(seen, submatch(1)) ? '' : execute('let seen[submatch(1)] = 1').submatch(0) /

This leaves the first occurrence. It would be better to write a function if this is to be a commonly used operation.