[R] Q re iterating a process and appending results to output file

[Eric C Banfield]

Jim, thank you very much  This looks like it works.
(I just need to study the code and see if I can understand precisely why
and how it works.)
Eric




                                                                           
                                                                           
             "jim holtman"                                                 
             <jholtman at gmail.c                                             
             om>                                                        To 
                                                                           
             07/23/2008 02:56          "Eric C Banfield" <ECB2 at ntrs.com>   
             PM                                                         cc 
                                       r-help at r-project.org                
                                                                   Subject 
                                       Re: [R] Q re iterating a process    
                                       and appending results to output     
                                       file                                
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           
                                                                           



Here is one way of doing it:

# generate 200 x 2500 samples and then check them
c <- qnorm(0.05)
i <- 2500
iter <- 200
x <- matrix(rnorm(i * iter, 0, 1) < c,nrow=i)  # TRUE/FALSE according
to condition
# now create the counts
x.c <- colSums(x)
# write out to a file 1 value on each line
cat(x.c, file='/tempxx.txt', sep="\n")


On Wed, Jul 23, 2008 at 2:47 PM, Eric C Banfield <ECB2 at ntrs.com> wrote:
>
> Greetings.  This is very basic but we can't figure it out.  The following
> simple code counts how many values land in the "tail" (below a quantile)
of
> a standardized normal distribution of random numbers.  First two commands
> are inputs:
>> c <-0.05
>> i <-2500
> Second two commands are formulas I want to repeat many times (sort of
like
> an Excel/VBA macro) using those same inputs:
>> r <- rnorm(i,0,1)
>> n <- length(r[r<qnorm(c)])
>
> I believe I could also run this as one line: r <- rnorm(i); n <-
> length(r[r<qnorm(c)])
>
> "n" will vary around 125.  Each time I run the code -- say 262 times --
> I'll get a new "n".  I want to save all those "n"s in a file for Excel.
>
> I can use cat(n,file="c:/temp/file.csv") to store the value of n in a
*.csv
> file.  But:
>
> 1. How do I tell R each time I run the above to append in that file the
new
> value of 'n' to the list of prior 'n's?
> e.g., Suppose the first run I get n=125, second run I get n=127, and so
on.
> I want a file that will have 125 in the first row, 127 the second, and so
> on,
> I tried cat(n,file="c:/temp/file.csv", sep=" ") but it holds only the
> single, latest value of n.
> I tried file.append but then I get 125127.
>
> 2.  How do I tell R to run or loop through the above lines hundreds of
> times, e.g., j = 262? -- rather like an Excel/VBA macro?)
> So if I can make this iterate 262 times, I'll have a list or column of
262
> numbers.
>
> Thanks -- Eric.
>
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>



--
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?