df[ order(row.names(df)),]

A    B    C    D    E
1     13    6    4    4    3
10    16    5    3    8    3
100    6    4   12   14    5
101    2   14   15    3   10
102    5    2    2    9    5
103    9    1   12    3   15
104   15    1    1    8    2
105    2   10   14    7    4
106    6    2   10    2    9
107    3    1    1    3   22
108   11    4    1    6   15
109    4   29    2    6    2
11     6   29    1    4    1

row.names(df) <- attr(df, "row.names")
row.names(df) <- as.numeric(row.names(df))

[1] "character"           "vector"              "data.frameRowLabels" "SuperClassMethod"