Rounding output from by function in R

Question

I'm trying to round an output from a simple by() function in R. This is what I have:

> by(glaciers[,1:3],glaciers$activity.level,mean)

glaciers$activity.level: Active
       aspect  sun.duration      latitude 
-9.444444e+00  1.771778e+03  3.247643e+09 
-------------------------------------------
glaciers$activity.level: Inactive
      aspect sun.duration     latitude 
1.041667e+01 2.067583e+03 4.048301e+09 
-------------------------------------------
glaciers$activity.level: Relict
      aspect sun.duration     latitude 
1.766667e+01 2.168000e+03 2.759283e+09 

How can I get my output to round to say 5 decimal places, and still keep the factors?

I've tried: round(by(glaciers[,1:3],glaciers$activity.level,mean),5) but get an error: Non-numeric argument to mathematical function.

Answer 1

If you already have the output saved to a variable, say x:

x <- by(glaciers[,1:3],glaciers$activity.level,mean)

Then apply round() to each element (the output of by() in this case is a list).

x[] <- lapply(x,round,5)
x

reassigning to x[] rather than x allows x to retain attributes attached to it from by().

Edit: round() actually changes the value of the variables but is decoupled from its printing. If you want to suppress the scientific notation output format, use format="f" argument to formatC()

> round(1.2345e10,5)
[1] 1.2345e+10
> formatC(1.2345e10,digits=5,format="f")
[1] "12345000000.00000"

So the correction to the expression originally posted would be

x[] <- lapply(x,formatC,digits=5,format="f")