How to order my dataframe lexicographicaly

Question

I have a following data frame

a = data.frame(a=c(1,2,3,4,5,6,7),b=c(1,2,3,10,12,21,4),c=c(1,2,10,11,\"X\",\"Y\",3))
> a
  a  b  c
1 1  1  1
2 2  2  2
3 3         


        

Answer 1

Assuming these are human chromosome names, chr1...chr22, chrX, chrY. We can convert them to numeric, then use order:

# convert to numeric
a$chromN <- as.integer(ifelse(a$c == "X", "23", ifelse(a$c == "Y", "24", a$c)))

# now sort as usual:
a[ order(a$chromN), ]

#   a  b  c chromN
# 1 1  1  1      1
# 3 3  3 10      2
# 4 4 10 11      3
# 2 2  2  2      4
# 7 7  4  3      5
# 5 5 12  X     23
# 6 6 21  Y     24