Loop through and subtract two columns in R - r

Question

I have a df that looks like this:
Year Subscribers Forecast AbsError
1 2006 23188171 0 0
2 2007 28745769 0 0
3 2008 34880964 0 0
4 2009 46373266 0 0
I have a lop that fills in the forecast column and then it should subtract the subscriber value from the forecast value and put that number into the AbsError column, like so:
Year Subscribers Forecast AbsError
1 2006 23188171 9680000 13508171
2 2007 28745769 27960000 46240000
3 2008 3488096 46240000 11359036
My Loop looks like this:
for (i in 1:nrow(new.phone)) {
new.phone$Forecast[i] <- ((1.828e+07 )*new.phone$Year[i]) + (-3.666e+10)
new.phone$AbsError <- abs((new.phone$Subscribers[i] - new.phone$Forecast[i]))
}
Although this loop is giving the correct forecasted values, its giving the incorrect AbsError values, but i cannot figure out why. All the AbsError values are 10464033, but that is wrong. Any ideas why this is?
Thanks for the help!

Answer 1

You don't need a for loop to do that. This does what you need:
new.phone$Forecast <- ((1.828e+07) * new.phone$Year) + (-3.666e+10)
new.phone$AbsError <- abs(new.phone$Subscribers - new.phone$Forecast)

Answer 2

You were just missing the index in the second line of the loop. Should be: new.phone$AbsError[i] <- [...] not new.phone$AbsError <- [...].
Anyway, you could skip the loop of you want:
new.phone$Forecast <- (1.828e+07) * new.phone$Year + (-3.666e+10)
new.phone$AbsError <- abs(new.phone$Subscribers - new.phone$Forecast)
new.phone
Year Subscribers Forecast AbsError
1 2006 23188171 9680000 13508171
2 2007 28745769 27960000 785769
3 2008 34880964 46240000 11359036
4 2009 46373266 64520000 18146734

Answer 3

Try this in dplyr:
require(dplyr)
k <- read.table(text = "Year Subscribers Forecast AbsError
1 2006 23188171 0 0
2 2007 28745769 0 0
3 2008 34880964 0 0
4 2009 46373266 0 0")
k%>%mutate(Forecast = ((1.828e+07 )*Year) + (-3.666e+10) )%>%
mutate(AbsError = abs(Subscribers-Forecast))
Results:
Year Subscribers Forecast AbsError
1 2006 23188171 9680000 13508171
2 2007 28745769 27960000 785769
3 2008 34880964 46240000 11359036
4 2009 46373266 64520000 18146734