R help - Jul 2008 - Q re iterating a process and appending results to output file

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.

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.
>
> ______________________________________________
> R-help at r-project.org 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.
>


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

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