The boot() function in the 'boot' package expects to find a function
for the statistic with two arguments: The data object plus a row index object.
You don't indicate enough to see how you will be resampling. It you
sum all elements in your table, resampling would have to be one of:
1. A sample with replacement of rows, or
2. A sample with replacement of columns, or
3. A sample with replacement of elements in the whole table.
Assuming you want sampling with replacement of rows:
sumf<- function (x, i) { sum(x[i,]) }
result<- boot(mytable, sumf, 1000)
boot.ci(result, type='bca')
A simulation:
> mytable<- matrix(rnorm(2000), ncol=20)
> sum(mytable)
[1] -14.92842
> sumf<- function(x,i) sum(x[i,])
> require('boot')
Loading required package: boot
> b1<- boot(mytable, sumf, 1000)
> boot.ci(b1, type='bca')
BOOTSTRAP CONFIDENCE INTERVAL CALCULATIONS
Based on 1000 bootstrap replicates
CALL :
boot.ci(boot.out = b1, type = "bca")
Intervals :
Level BCa
95% (-101.49, 85.20 )
Calculations and Intervals on Original Scale
At 01:28 PM 2/25/2010, xonix wrote:
Hi all
Forgive me, I'm a total R newbie, and this seems to be a straightforward
simple bootstrap problem, but after a whole day of trying to figure out how
to do it I'm ready to give up. Part of the problem is that every example and
every help page seems to be about doing something more far more complex.
I'm got a table with 40 columns and 750 rows. I sum all the values across
the whole table (and subsets of the columns). I want to bootstrap to get the
95% confidence intervals for that sum value.
result <- boot(table, <function>, 1000)
boot.ci (result, bca)
It seems to me that the 'function' is something to sum all the columns and
rows of the table (or a subset should I desire). I've tried writing 'sum'
for the function, but this gives me a huge figure which can't possibly be
right.
================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS e-mail: r...@lcfltd.com
Least Cost Formulations, Ltd. URL: http://lcfltd.com/
824 Timberlake Drive Tel: 757-467-0954
Virginia Beach, VA 23464-3239 Fax: 757-467-2947
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