[R] How to signal the end of the table?

[Uwe Ligges]

What about trying to use a database system and make queries?
If you are at the end of a file, you will read elements of length 0...

Uwe Ligges



Yuchen Luo wrote:
> I am using a "for" loop to read a table row by row and I have to specify how
> many records are there in the table. I need to read row by row because the
> table is huge and the memory not large enough for the whole table.:
> 
> 
> 
> number.of.records=100
> 
> 
> 
> fp=file("abc.csv","r")
> 
> pos=seek(fp, rw="read")
> 
> for (i in 1:number.of.record){
> 
> current.row=scan(file=fp, sep=',', what=list(count=1, cusip6="", idate=1,
> spread=1.1, vol252=1.1, vol1000=1.1, st_debt=1.1, lt_debt=1.1 , total_liab=
> 1.1, cr=1.1,   shrout=1.1, prc=1.1, mkt_cap=1.1, rtng=1.1, sec=1.1, cr3m=1.1,
> cr5y=1.1, ust3m=1.1,  ust5y=1.1), flush=TRUE, nlines=1,quiet=T)
> 
> ...
> 
> }
> 
> 
> 
> I need to know the number of records in the table and put it in the variable
> named "number.of.records". When I have a new table that I do not know how
> many records it has, I use excel to open the file to figure it out and put
> it in variable " number.of.records". I often have many tables to try and
> every one of them has thousands of records----it takes a lot of time and
> trouble to adjust the code every time I read a different table.
> 
> 
> 
> I am wondering if I can change the "for" loop to a "while" loop:
> 
> 
> 
> while (the end of the table has not been reached)
> 
> {
> 
> current.row=scan(file=fp, sep=',', what=list(count=1, cusip6="", idate=1,
> spread=1.1, vol252=1.1, vol1000=1.1, st_debt=1.1, lt_debt=1.1 , total_liab=
> 1.1, cr=1.1,   shrout=1.1, prc=1.1, mkt_cap=1.1, rtng=1.1, sec=1.1, cr3m=1.1,
> cr5y=1.1, ust3m=1.1,  ust5y=1.1), flush=TRUE, nlines=1,quiet=T)
> 
> ...
> 
> }
> 
> 
> The problem is how to articulate "while (the end of the table has not been
> reached)", or equivalently, how to signal the end of the table?
> 
> Best Wishes
> Yuchen Luo
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.