[R] Questions about sort data

[Xiao Zhao]

Dear R users,
I am doing my project which I want to plot a piecewise function, I knew
that I can use the command segments to plot. But the problem is I want
to use my real data which needs me to sort of my data by using the 'if
else'command, I use it 
If(t[i]<36) lambda<-0.5
Else lambda<-0.2
The funny thing is when I look at my data set, it did not follow my
command to sort data, also the final numbers do not change either.
The other problem is I have a big data set, sometimes I want to know the
number of some data, such as how many numbers are over 60, how to do
this by using R?
Does anybody got any ideas about my two pros?

Thank you in advance
Best wishes
Nessie^_^