isA=c("yes","no","yes",NA)
isB=c("no","yes","no",NA)
df <- data.frame(isA,isB)
df   isA  isB
1  yes   no
2   no  yes
3  yes   no
4 <NA> <NA>df$ans<-apply(df,1,function(x) table(x)["yes"])
df
   isA  isB ans
1  yes   no   1
2   no  yes   1
3  yes   no   1
4 <NA> <NA>  NA

1. df[df["val"]==0].id.count()
2. len(df[df["val"]==0])

isA=c(1,2,3,NA)
isB=c(11,12,13,NA)
df <- data.frame(isA,isB)
df
  isA isB
1   1  11
2   2  12
3   3  13
4  NA  NA
 

df$ans<-apply(df,1,function(x) sum(x>=1))
df
  isA isB ans
1   1  11   2
2   2  12   2
3   3  13   2
4  NA  NA  NA