Hi R users,
I have been struggling to select the equal number of samples from each strata.
I have the data collected in different years in different regions with
different sample size. Basically, I have two two conditions (year and region).
I wanted to make smaple sample size for both year and region.
I found that "strata.sampling' package can use if I had one condition, but I
have two conditions . Is there any package from which I can put two conditions
and select the rows randomly 999 times and put the mean value?
Your help would be really appreciated. I am spending so much time...
Here What I did for the example data
raw=structure(list(watershed = structure(c(1L, 1L, 1L, 1L, 1L, 1L,
1L, 2L, 2L, 2L, 2L, 2L, 2L), .Label = c("A", "B"), class = "factor"),
year = c(2001, 2001, 2002, 2002, 2002, 2002, 2002, 2001,
2001, 2001, 2002, 2002, 2002), sp1 = c(18.38, 29.1, 90.72,
16.12, 49.12, 20.81, 65.1, 1.87, 72.99, 93.45, 38.44, 67.13,
45.71), sp2 = c(46.46, 94, 86.87, 46.91, 21.41, 92.82, 87.75,
16.18, 18.16, 18.76, 19.26, 52.73, 49.09), sp3 = c(86.9,
62.82, 74.32, 75.49, 20.17, 58.84, 16.51, 44.14, 44.39, 32.36,
53.28, 67.42, 33.37)), .Names = c("watershed", "year", "sp1",
"sp2", "sp3"), class = "data.frame", row.names = c(NA, -13L))
require(sampling)
if (is.null(method)) method <- "srswor"
if (!method %in% c("srswor", "srswr"))
stop('method must be "srswor" or "srswr"')
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)
}
test1<-strata.sampling(raw, ("watershed"), 2)# select 2 rows by watershed
BUT, I wanted to use "year" too. ("watershed", "year"). When I added the
"year", it did not work
test1<-strata.sampling(raw, ("watershed", "year"), 2)# select 2 rows by
watershed and year
> test1<-strata.sampling(raw, ("watershed", "year"), 2)
Error: unexpected ',' in "test1<-strata.sampling(raw, ("watershed","
Here I want to select rows using tow conditions ("watershed", "year") with 999
times and put mean value of sp1,sp2,sp3, using random sampling 999. here is the
output I wanted
output<-structure(list(watershed = structure(c(1L, 1L, 2L, 2L), .Label = c("A",
"B"), class = "factor"), year = c(2001L, 2002L, 2001L, 2002L),
sp1 = structure(c(1L, 1L, 1L, 1L), .Label = "mean", class = "factor"),
sp2 = structure(c(1L, 1L, 1L, 1L), .Label = "mean", class = "factor"),
sp3 = structure(c(1L, 1L, 1L, 1L), .Label = "mean", class = "factor")),
.Names = c("watershed",
"year", "sp1", "sp2", "sp3"), class = "data.frame", row.names = c(NA,
-4L))
Any suggestions?
Thanks for your help.
KG
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