## ST101 Homework in R

04 Jul 2012As part of Udacity’s ST101, I’ve started completing the homeworks in R using RStudio. Below is the solution for homework 2.6:

```
print.matrix <- function(m){
write.table(format(m, justify="right"),
row.names=T, col.names=T, quote=F)
}
p_loaded = 0.1
p_hfair = 0.5
p_hloaded = 0.9
cells <- c(4, 0,10, 0, 20, 0, 0, 5, 2, 3)
rnames <- c("# heads", "# tails")
# creates a list of in form ("#1", "#2", "#n"...) to n=number of trials
cnames <- c(paste("#", 1:(length(cells)/2), sep = ""))
trials <- matrix(cells, nrow=2, ncol=5, byrow=FALSE, dimnames=list(rnames, cnames))
#print(trials)
# P(fair|flips) = (P(flips|fair) * P(fair))/ P(flips)
for (trial in 1:ncol(trials)) {
# joint probablities for fair and loaded coins given observed results
jp_fair = trials[1, trial] * p_hfair + trials[2, trial] * (1-p_hfair)
jp_loaded = trials[1, trial] * p_hloaded + trials[2, trial] * (1-p_hloaded)
if (jp_fair < jp_loaded) {
print(paste("trial ", trial, " is < 0.5 probable for a fair coin!", sep=""))
}
}
```