[R] Setting up a blank table with column names in the hard drive

[Duncan Murdoch]

Yuchen Luo wrote:
> Dear Friends.
> Greetings!
>
> This should be a very common operation and I believe there should be a nice
> way in R to handle it.  I couldn't find it in the manual or by searching on
> line. I am wondering if I could ask for some help in this community.
>
>
>
> I am trying to record the results of my program to a csv file in the hard
> drive so as to save memory space and also to read the results in excel after
> running the program.  Every loop of my program will result in a list with
> element belonging to different class. For example, things like
>
>
>
> a1 <- list(name="Fred", wife="Mary", no.children=3)
> a2 <- list(name="Tom", wife="Joy", no.children=9)
> a3 <- list(name="Paul", wife="Alic", no.children=5)
>
>
>
> I want the columns to have titles, in the example above, I want to see the
> title "name", "wife" and "no.children" in the excel file.
>
>
>
> To set up the table in the csv file, I need to add at least one row in the
> table up front. How ever, I do not have the first loop of the program
> completed yet at that time. If I add a row that is meaningless, how may I
> delete it after all the loops are completed and all the meaningful rows are
> added to the table?
>
>   
I'd use data frames rather than plain lists for the results, so 
write.csv will work.

Create a data frame with 0 rows, and write it out:  this will give you 
your header line.

e.g.

blank <- data.frame(name=character(0), wife=character(0), 
no.children=numeric(0))
write.csv(blank, 'file.csv')

Now you can rbind new lines onto the data frame as you calculate new 
records and rewrite the whole thing, or just append them to the file 
with append=TRUE and writing with col.names=FALSE.

Duncan Murdoch