R: What are the best functions to deal with concatenating and averaging values in a data.frame?

Question

I have a data.frame from this code:

   my_df = data.frame(\"read_time\" = c(\"2010-02-15\", \"2010-02-15\", 
                                      \"2010-02-         


        

Answer 1

This illustrates how you could use aggregate to get the mean and standard deviation by your read_time.

>aggregate(my_df$OD, by=list(my_df$read_time), function(x) mean(x))

     Group.1         x
1 2010-02-15 0.1500000
2 2010-02-16 0.2333333
3 2010-02-17 0.5000000


>aggregate(my_df$OD, by=list(my_df$read_time), function(x) sd(x))
     Group.1          x
1 2010-02-15 0.07071068
2 2010-02-16 0.15275252
3 2010-02-17         NA