keep rows with at least one non-missing value #

keepRowsWithNonMissingValues

# adapted from: https://stackoverflow.com/questions/44077122/r-select-rows-with-non-na-values-in-at-least-one-of-the-four-columns 

a<-c(NA,NA,NA,NA,2,5,4,3,NA,NA)
b<-c(NA,NA,NA,NA,2,3,4,5,NA,NA)
c<-c(NA,NA,NA,NA,NA,NA,NA,NA,NA,NA)
d<-c(1,4,3,1,2,4,3,2,1,NA)
df<-cbind(a,b,c,d)
df_atLeastOneNonMissingValue <- df[rowSums(is.na(df)) != ncol(df),] ## just to keep rows with at least one non-missing value 
nrow(df)
nrow(df_atLeastOneNonMissingValue)

# with selected rows: 
df_atLeastOneNonMissingValueInFirstThreeColumns <- df[rowSums(is.na(df[, c("a","b","c")])) != 3,]
nrow(df_atLeastOneNonMissingValueInFirstThreeColumns)