On 03/31/2015 01:44 PM, Duncan Murdoch wrote:
On 31/03/2015 1:05 PM, Kevin E. Thorpe wrote:
Hello.
I am trying to simulate recruitment in a randomized trial. Suppose I
have three streams (strata) of patients represented by these data frames.
df1 <- data.frame(strat=rep(1,10),id=1:10,pid=1001:1010)
df2 <- data.frame(strat=rep(2,10),id=1:10,pid=2001:2010)
df3 <- data.frame(strat=rep(3,10),id=1:10,pid=3001:3010)
What I need to do is construct a data frame with all of these combined
where the order of selection from one of the three data frames is
randomized but once a stratum is selected patients are selected
sequentially from that data frame.
To see what I'm looking to achieve, suppose the first five subjects were
to come, in order, from strata (data frames) 1, 2, 1, 3 and 2. The
expected result should look like this:
rbind(df1[1,],df2[1,],df1[2,],df3[1,],df2[2,])
strat id pid
1 1 1 1001
2 2 1 2001
21 1 2 1002
4 3 1 3001
22 2 2 2002
I hope what I'm trying to accomplish makes sense. Maybe I'm missing
something obvious, but I really have no idea at the moment how to
achieve this elegantly. Since I need to simulate many trial recruitments
it needs to be general and compact.
I appreciate any advice.
How about something like this:
# Permute an ordered vector of selections:
sel <- sample(c(rep(1, nrow(df1)), rep(2, nrow(df2)), rep(3, nrow(df3))))
# Create an empty dataframe to hold the results
df <- data.frame(strat=NA, id=NA, pid=NA)[rep(1, length(sel)),]
# Put the original dataframes into the appropriate slots:
df[sel == 1,] <- df1
df[sel == 2,] <- df2
df[sel == 3,] <- df3
# Clean up the rownames
rownames(df) <- NULL
Duncan Murdoch
Thanks Duncan.
Once you see the solution it is indeed obvious.
Kevin
--
Kevin E. Thorpe
Head of Biostatistics, Applied Health Research Centre (AHRC)
Li Ka Shing Knowledge Institute of St. Michael's
Assistant Professor, Dalla Lana School of Public Health
University of Toronto
email: kevin.tho...@utoronto.ca Tel: 416.864.5776 Fax: 416.864.3016
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