Re: [R] subsamples and regressions for 100 times

[Michael Dewey]

Comment inline

On 17/02/2015 12:40, Angela Smith wrote:


Hi R user,
I'm new to R so
my problem is probably pretty simple but I'm stuck:



my data is consist of 2 variables: co2, temp and one
treatment (l_group). The sample size is different among the treatments. so

that, I wanted to make equal sample size among three groups (A,B and C) of the
treatment.


Not sure whether that is necessary for regression but you did not tell 
us why you want to do that.

For this one, I used subsamples technique. Using
subsample, each time the data are different among the three groups of the
treatment.

so that I want to run regression (co2~temp) for a 100
subsamples for each group of treatment (100 times subsample).


The usual way to do this is to store the subsamples in a list and then 
write a function and use lapply, say to store your models. You then have 
another list to which you can then apply the extractor function of your 
choice.


it means that I will have 100 regression equations.  Later, I want to compare 
the slope of the
regression among the three groups. is there simple way to make a loop so that I
can compare it?

Thanks in advance!



Angela

================
Here is the example:

dat<-structure(list(co2 = c(0.15, 0.148, 0.125, 0.145, 0.138, 0.23,
0.26, 0.35, 0.41, 0.45, 0.39, 0.42, 0.4, 0.43, 0.26, 0.3, 0.34,
0.141, 0.145, 0.153, 0.151, 0.128, 0.23, 0.26), temp = c(0.0119,
0.0122, 0.0089, 0.0115, 0.0101, 0.055, 0.097, 0.22, 0.339, 0.397,
0.257, 0.434, 0.318, 0.395, 0.087, 0.13, 0.154, 0.0107, 0.0112,
0.0119, 0.012, 0.0092, 0.055, 0.089), L_group = structure(c(1L,
1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L,
3L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("A", "B", "C"), class = "factor")), .Names = 
c("co2",
"temp", "L_group"), class = "data.frame", row.names = c(NA, -24L
))

head(dat)
library(sampling)

# strata.sampling -----
strata.sampling <- function(data, group,size, method = NULL) {
  require(sampling)
   if (is.null(method)) method <- "srswor"
   temp <- data[order(data[[group]]), ]
   ifelse(length(size)> 1,
          size <- size,
          ifelse(size < 1,
                 size <- round(table(temp[group]) * size),
                 size <- rep(size, times=length(table(temp[group])))))
   strat = strata(temp, stratanames = names(temp[group]),
                  size = size, method = method)
   getdata(temp, strat)
}

#--------------------------------------------------
sub_dat <- strata.sampling(dat, 'L_group', 4)#
Lmodel_subdata1<-lm(co2~temp, data=subdat)
Lmodel_subdata1#coef

sub_dat2 <- strata.sampling(dat, 'L_group', 4)#
Lmodel_subdata2<-lm(co2~temp, data=subdat2)
Lmodel_subdata2#coef

and so on.....[for 100 times)

Table<-rbind(Lmodel_subdata1$coef, Lmodel_subdata1$coef, ....)


                                        
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--
Michael
http://www.dewey.myzen.co.uk

______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.