Question

I made a small example for my data:

mth <- c(rep(1,10))  
day <- c(rep(10,5),rep(11,5))  
hr <- c(3,4,5,6,7,3,4,5,6,7)  
v <- c(3,4,5,4,3,3,4,5,4,3)  
A <- data.frame(cbind(mth,day,hr,v)) 

What I need to do is to get how many value < 4 on a daily basis, I tried to use the function rle, but was not able to get what I need. The output should look like:

mth <- c(rep(1,2))  
day <- c(10,11)  
v <- c(2,2)  #each 2 here is the sum of 1(3)+1(3) for Oct. and Nov.  
A <- data.frame(cbind(mth,day,v))  

Thank you for your help!

Answer 1

With ddply it’s easy

library(plyr)
ddply(A, .(mth, day), function(x)  sum(x$v<4))
#    mth day V1
# 1   1  10  2
# 2   1  11  2

or you could use summarize

ddply(A, .(mth, day), summarize, less4 = sum(v <4))
#   mth day less4
# 1   1  10  2
# 2   1  11  2