why the same values cannot be judged to be the same in R
On Nov 12, 2009, at 10:04 PM, rusers.sh wrote:
Hi Rusers,
I found sometimes that the same values cannot be judged to be the
same in
R. Anybody knows the probelm? I think i ignored some minor detail.
Thanks.
Here is the example.
############
data1<-matrix(data=c(1,1.2,1.3,"3/23/2004",1,1.5,2.3,"3/22/2004",
2,0.2,3.3,"4/23/2004",3,1.5,1.3,"5/22/2004"),nrow=4,ncol=4,byrow=TRUE)
data1<-data.frame(data1);names(data1)<-c("areaid","x","y","date")
data2<-matrix(data=c(1,1.22,1.32,1, 1.53, 2.34,1, 1.21, 1.37,1,
1.52,
2.35,2, 0.21, 3.33,2, 0.23, 3.35,3, 1.57, 1.31,3, 1.59,
1.33),nrow=8,ncol=3,byrow=TRUE)
data2<-data.frame(data2);names(data2)<-c("areaid","x1","y1")
data2$tag<-0
data1_1<-data1[1,]
data2_1<-data2[data2$areaid==data1_1$areaid & data2$tag==0,]
ran_1<-sample(c(1:length(data2_1)),2, replace = FALSE)
data2_1<-data2_1[ran_1,]
data_1<-merge(data1_1,data2_1)
#data_1
# areaid x y date x1 y1 tag
# 1 1 1.2 1.3 3/23/2004 1.52 2.35 0
# 2 1 1.2 1.3 3/23/2004 1.53 2.34 0
data2[data_1$x1==data2$x1 & data_1$y1==data2$y1 & data2$tag==0,]
#data2[c(data_1$x1==data2$x1 & data_1$y1==data2$y1 & data2$tag==0),]
I suspect your use of multiple logical tests across two different dataframes with different numbers of rows may not be giving you the results you expect: > data_1$x1==data2$x1 [1] FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE > data_1$y1==data2$y1 [1] FALSE FALSE FALSE TRUE FALSE FALSE FALSE FALSE > data2$tag==0 [1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE # So that test is doing nothing > data2$y1 [1] 1.32 2.34 1.37 2.35 3.33 3.35 1.31 1.33 > data_1$y1 [1] 2.34 2.35 Perhaps you ought to look at the dyadic function %in% as a substitute for "==" ?"%in%"
# areaid x1 y1 tag #2 1 1.53 2.34 0 There should be two same observations between data_1 and data2, but here only one was identified.
If the above commentary did not clarify what was happening, then can you explain in more detail what (and why) you were doing at each step and what you expected to get in the end. The phrase "two same observations between data_1 and data2" does not seem to be an unambiguous expression. I cannot think of any natural ordering to these rows of cases, so the notion of "between" does not seem appropriate.
David Winsemius, MD Heritage Laboratories West Hartford, CT