Generate a dummy-variable

Question

I have trouble generating the following dummy-variables in R:

I\'m analyzing yearly time series data (time period 1948-2009). I have two questions:

1. <

Answer 1

What I normally do to work with this kind of dummy variables is:

(1) how do I generate a dummy variable for observation #10, i.e. for year 1957 (value = 1 at 1957 and zero otherwise)

data$factor_year_1 <- factor ( with ( data, ifelse ( ( year == 1957 ), 1 , 0 ) ) )

(2) how do I generate a dummy-variable which is zero before 1957 and takes the value 1 from 1957 and onwards to 2009?

data$factor_year_2 <- factor ( with ( data, ifelse ( ( year < 1957 ), 0 , 1 ) ) )

Then, I can introduce this factor as a dummy variable in my models. For example, to see whether there is a long-term trend in a varible y :

summary ( lm ( y ~ t,  data = data ) )

Hope this helps!