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

The simplest way to produce these dummy variables is something like the following:

> print(year)
[1] 1956 1957 1957 1958 1958 1959
> dummy <- as.numeric(year == 1957)
> print(dummy)
[1] 0 1 1 0 0 0
> dummy2 <- as.numeric(year >= 1957)
> print(dummy2)
[1] 0 1 1 1 1 1

More generally, you can use ifelse to choose between two values depending on a condition. So if instead of a 0-1 dummy variable, for some reason you wanted to use, say, 4 and 7, you could use ifelse(year == 1957, 4, 7).