Change column values based on factors of other columns - r

Question

For example, if I have a data frame like this:
df <- data.frame(profit=c(10,10,10), year=c(2010,2011,2012))
profit year
10 2010
10 2011
10 2012
I want to change the value of profit according to the year. For year 2010, I multiple the profit by 3, for year 2011, multiple the profit by 4, for year 2012, multiple by 5, which should result like this:
profit year
30 2010
40 2011
50 2012
How should I approach this? I tried:
inflationtransform <- function(k,v) {
switch(k,
2010,v<-v*3,
2011,v<-v*4,
2012,v<-v*5,
)
}
df$profit <- sapply(df$year,df$profit,inflationtransform)
But it doesn't work. Can someone tell me what to do?

Answer 1

For this particular example, since your factors and years are both ordered and incremented by 1, you could just subtract 2007 from the year column and multiply it by profit.
transform(df, profit = profit * (year - 2007))
# profit year
# 1 30 2010
# 2 40 2011
# 3 50 2012
Otherwise, you could use a lookup vector. This will cover all cases.
lookup <- c("2010" = 3, "2011" = 4, "2012" = 5)
transform(df, profit = profit * lookup[as.character(year)])
# profit year
# 1 30 2010
# 2 40 2011
# 3 50 2012
I wouldn't use switch() unless you really need to. It's not vectorized, and that's where R is most efficient. However, since you ask for it in the comments, here's one way. I find it easier to use a for() loop with switch().
for(i in seq_len(nrow(df))) {
df$profit[i] <- with(df, switch(as.character(year[i]),
"2010" = 3 * profit[i],
"2011" = 4 * profit[i],
"2012" = 5 * profit[i]
))
}