id bin_1 bin_2 bin_3 bin_4 bin_5 bin_6 bin_7 bin_8 bin_9
1   a     b     c     d     e     na    na    na    na
2   a     b     na    na    na    na    na    na    na

id reversed_noNAs
1      edcba
2      ba

do.call(paste, c(df[c("bin_1", "bin_2", "bin_3", "bin_4", "bin_5", "bin_6","bin_7","bin_8","bin_9")], sep = ""))

apply(
    X=df[, grepl('^bin_\d+$', names(df))],
    MARGIN=1,
    FUN=function(x) {paste(rev(na.omit(x)), collapse='')}
)

apply(
    X=df[, grepl('^bin_\d+$', names(df))],
    MARGIN=1,
    FUN=function(x) {paste(rev(sub('^NA$', '', x)), collapse='')}
)

df = data.frame(matrix(sample(letters[1:5], 100, replace = TRUE), 10, 10))
na_rows = sample(1:10, 5)
na_cols = sample(1:10, 5)
df[sort(na_rows), sort(na_cols)] <- NA

apply(df, 1, function(x) paste(na.omit(rev(x)), collapse = ''))