Set up needed files and objects

getwd()    # Get current working directory

## [1] "C:/Users/Juan Steibel/AppData/Local/Temp/RtmpSSuXJB"

#setwd("C:/Users/steibelj/OneDrive/Documents/job/ans824/2015")    # Set current working 
setwd("C:/Users/Juan Steibel/SkyDrive/Documents/job/ans824/2015")

rm(list=ls())       # Remove all objects from work environment

cnt<-read.table("counts.txt",header=T)

Problem 3

Alternative activity

code to make loopless

mcnt<-as.matrix(cnt)
mean_cnt<-matrix(0,nrow(cnt),24)
var_cnt<-matrix(0,nrow(cnt),24)

# 1) we need a loop over the rows of cnt:
system.time({
for (i in 1:nrow(cnt)) { #this is a loop from 1 to the number of rows of cnt
  # 2) we now transform the row of 96 observations into a matrix of 4 by 24:
  vec_count<-matrix(mcnt[i,],4,24,byrow=F) #notice we need to fill the matrix
  #column wise
  #notice unlist, necesary to get correct format
  # 3) now we compute the column means
  mean_sample<-colMeans(vec_count)
  # 4) now we compute the column variances (diagonal of variance-covariance matrix)
  var_sample<-diag(var(vec_count))
  # 5) we "grow" the matrix of results
  mean_cnt[i,]<-mean_sample
  var_cnt[i,]<-var_sample
  # 6) close the loop and back
}
})

a function that will facilitate the implementation:

input
vec (a row of counts)
nrep (number of technical reps, by default 4)
operator (a text: mean or var)
restrictions:
vec should be numeric
length(vec)/nrep should be an integer number

compute_stat<-function(vec,nrep=4,operator="mean"){
  if (!is.vector(vec)) stop ("vec should be a vector")
  if (!is.numeric(vec)) stop ("vec should be numeric")
  if (!((length(vec)%%nrep)==0)) stop ("length of vec should be multiple of nrep")
  if ((operator!="mean")&(operator!="var")) stop ("operator should be either mean or var")
  nc<-length(vec)/nrep
  vec_count<-matrix(vec,nrep,nc,byrow=F)
  if (operator=="mean") {
    result<-colMeans(vec_count)
  } else {
    result<-diag(var(vec_count))
  }
  return(result)
}

sugested activities
-explain each step of the function
-apply the function and test it for accuracy

Lab 3 ANS 824

Set up needed files and objects

Problem 3