Here's another way:
With d1 as your data frame,
library(plyr)
d2 <- ddply(d1, .(fam), function(x) x[sample(nrow(x), 1), ])
d2[sample(nrow(d2), 2), ]
If you have to take account of the 'only one family' case, you
can wrap this in a function with an appropriate check:
fish <- function(d){
if(length(unique(d[,'fam'])) < 2) stop('only one family')
d2 <- ddply(d,.(fam),function(x)x[sample(nrow(x), 1), ])
d2[sample(nrow(d2), 2), ]
}
Peter Ehlers
On 2012-03-22 16:03, Jorge I Velez wrote:
You could avoid the loop to run for ever by introducing a stop() check.
Here is an example using Dr. Savicky's code:
# function to sample B pairs of
# fishes from different families
# -- d has columns fam, born, spawn
foo<- function(d, B){
# internal function
foo<- function(d){
if(length(unique(d[, 'fam']))< 2) stop('only one family!')
while (1) {
ran<- sample(NROW(d), size = 2)
if (d[ran[1], 1] != d[ran[2], 1]) break
}
d[ran, ]
}
# sampling B pairs of fishes
lapply(1:B, function(i) foo(d))
}
# example: 2 pairs of fishes from different families
foo(fish, 2)
# data with only one family
ff<- fish[1,]
foo(ff, 2) # Error in foo(d) : only one family!
HTH,
Jorge.-
On Thu, Mar 22, 2012 at 5:27 PM, Petr Savicky<> wrote:
On Thu, Mar 22, 2012 at 11:42:53AM -0700, aly wrote:
Hi,
I want to randomly pick 2 fish born the same day but I need those
individuals to be from different families. My table includes 1787 fish
distributed in 948 families. An example of a subset of fish born in one
specific day would look like:
fish
fam born spawn
25 46 43
25 46 56
26 46 50
43 46 43
131 46 43
133 46 64
136 46 43
136 46 42
136 46 50
136 46 85
137 46 64
142 46 85
144 46 56
144 46 64
144 46 78
144 46 85
145 46 64
146 46 64
147 46 64
148 46 78
149 46 43
149 46 98
149 46 85
150 46 64
150 46 78
150 46 85
151 46 43
152 46 78
153 46 43
156 46 43
157 46 91
158 46 42
Where "fam" is the family that fish belongs to, "born" is the day it was
born (in this case day 46), and "spawn" is the day it was spawned. I
want to
know if there is a correlation in the day of spawn between fish born the
same day but that are unrelated (not from the same family).
I want to randomly select two rows but they have to be from different
fam.
The fist part (random selection), I got it by doing:
ran<- sample(nrow (fish), size=2); ran
[1] 9 12
newfish<- fish [ran,]; newfish
fam born spawn
103 136 46 50
106 142 46 85
In this example I got two individuals from different families (good) but
I
will repeat the process many times and there's a chance that I get two
fish
from the same family (bad):
ran<-sample (nrow(fish), size=2);ran
[1] 26 25
newfish<-fish [ran,]; newfish
fam born spawn
127 150 46 85
126 150 46 78
I need a conditional but I have no clue on how to include it in the code.
Hi.
Try the following.
while (1) {
ran<- sample(nrow(fish), size=2)
if (fish[ran[1], 1] != fish[ran[2], 1]) break
}
fish[ran, ]
This will generate only pairs from different families. However,
note that the loop will run forever, if the data contain only
fish from one family.
Hope this helps.
Petr Savicky.
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
