How to create a stratified sample by state in R

Question

How can I create a stratified sample in R using the \"sampling\" package? My dataset has 355,000 observations. The code works fine up to the last line. Below is the code I w

Answer 1

Without knowing of the strata function - a bit of coding might do what want:

d <- expand.grid(id = 1:35000, stratum = letters[1:10])

p = 0.1

dsample <- data.frame()

system.time(
for(i in levels(d$stratum)) {
  dsub <- subset(d, d$stratum == i)
  B = ceiling(nrow(dsub) * p)
  dsub <- dsub[sample(1:nrow(dsub), B), ]
  dsample <- rbind(dsample, dsub) 
  }
)

# size per stratum in resulting df is 10 % of original size:
table(dsample$stratum)

HTH, Kay

ps: CPU time on my relict laptop is 0.09!