Ordering Merged data frames - r

Question

As a fairly new R programmer I seem to have run into a strange problem - probably my inexperience with R
After reading and merging successive files into a single data frame, I find that order does not sort the data as expected.
I have multiple references in each file but each file refers to measurement data obtained at a different time.
Here's the code
library(reshape)
# Enter file name to Read & Save data
FileName=readline("Enter File name:\n")
# Find first occurance of file
for ( round1 in 1 : 6) {
ReadFile=paste(round1,"C_",FileName,"_Stats.csv", sep="")
if (file.exists(ReadFile))
break
}
x = data.frame(read.csv(ReadFile, header=TRUE),rnd=round1)
for ( round2 in (round1+1) : 6) {
#
ReadFile=paste(round2,"C_",FileName,"_Stats.csv", sep="")
if (file.exists(ReadFile)) {
y = data.frame(read.csv(ReadFile, header=TRUE),rnd = round2)
if (round2 == (round1 +1))
z=data.frame(merge(x,y,all=TRUE))
z=data.frame(merge(y,z,all=TRUE))
}
}
ordered = order(z$lab_id)
results = z[ordered,]
res = data.frame( lab=results[,"lab_id"],bw=results[,"ZBW"],wi=results[,"ZWI"],pf_zbw=0,pf_zwi=0,r = results[,"rnd"])
#
# Establish no of samples recorded
nsmpls = length(res[,c("lab")])
# Evaluate Z_scores for Between Lab Results
for ( i in 1 : nsmpls) {
if (res[i,"bw"] > 3 | res[i,"bw"] < -3)
res[i,"pf_zbw"]=1
}
# Evaluate Z_scores for Within Lab Results
for ( i in 1 : nsmpls) {
if (res[i,"wi"] > 3 | res[i,"wi"] < -3)
res[i,"pf_zwi"]=1
}
dd = melt(res, id=c("lab","r"), "pf_zbw")
b = cast(dd, lab ~ r)
If anyone could see why the ordering only works for about 55 of 70 records and could steer me in the right direction I would be obliged
Thanks very much

Answer 1

Check whether z$lab_id is a factor (with is.factor(z$lab_id)).
If it is, try
z$lab_id <- as.character(z$lab_id)
if it is supposed to be a character vector; or
z$lab_id <- as.numeric(as.character(z$lab_id))
if it is supposed to be a numeric vector.
Then order it again.
Ps. I had previously put these in the comments.