You probably want to start by organizing your data. Whether that be sorting or whatnot.

This really depends on the domain of data you're looking at but you might also look into converting data to fixed width rows.

For example:

Dan , 22,Farmer
Carson ,-01,Scientist

A very efficient way to check for negatives now appears where you can just check the [12] and/or [13] index of every row for a '-'

Though, I suspect your issues probably have more to do with polynomial or exponential complexity rather than linear

Might be helpful to include some sample data.