我如何使用 powershell 在大的 output 中的第一个负值。csv？

Question

I need to find the first negative value in a given column in huge (5 million line) .csv files.

Import-Csv .\filename.csv | select "column_header" -First 100 | Select-String '-'

works well enough, but there are 50 of these files and the -First 100 is occasionally more than -First 3000 . This is a job I'll have to do again as we add to it as well. I think the best thing to do would be to pipe this to a function that has some code that does:

while(!Found){
     if(value.beginsWith("-")) write-output(value); Found=true; break;
}

but I don't know how to stop the input to the pipe (if this is even a feasible way to do it.). It is important that we don't read through the entire file (but 5-10k lines would possibly work) - that takes FOREVER.

Answer 1

I believe this should get you the first negative result in "Column_Header" and stop after that. Not 100% this is the most efficient way tho, but it should work fine.

Import-Csv .\filename.csv | ?{[math]::Sign($_."column_header") -eq -1} | select -First 1

Some context for the math.Sign method: https://docs.microsoft.com/en-us/dotnet/api/system.math.sign?view=net-5.0

Returns:

Return value	Meaning
-1	value is less than zero.
0	value is equal to zero.
1	value is greater than zero.