Warning message: NAs introduced by coercion

Dear all,

I have a .csv file called df4. (15752 obs. of 264 variables).
I apply this code but couldn't continue further other analyses, a warning
message keeps coming up. Then, I want to determine max and min
similarity values,
heat map plot, cluster...etc

require(SNPRelate)
library(gdsfmt)
myd <- read.csv(file = "df4.csv", header = TRUE)
names(myd)[-1]

myd[,1]

myd[1:10, 1:10]

# the data must be 0,1,2 with 3 as missing so you have r

sample.id <- names(myd)[-1]
snp.id <- myd[,1]
snp.position <- 1:length(snp.id) # not needed for ibs
snp.chromosome <- rep(1, each=length(snp.id)) # not needed for ibs
snp.allele <- rep("A/G", length(snp.id)) # not needed for ibs

# genotype data must have - in 3

genod <- myd[,-1]
genod[is.na(genod)] <- 3
genod[genod=="0"] <- 0
genod[genod=="1"] <- 2
genod[1:10,1:10]
genod <- as.matrix(genod)
class(genod) <- "numeric"

*Warning message:In class(genod) <- "numeric" : NAs introduced by coercion*

Maybe I could illustrate more with details so I can be more specific?
Please, let me know.

I would appreciate your help.
Thanks,
Meriam