用缺失值重新编码R中的变量

Question

I'm having difficulty understanding why my code to create a dummy variable isn't working. My data contains some NA values and is of the following form:

Year   Month   Var1  Var2
2006    9      278   345
2006    10     251   857
2006    11     254   678
.      .       .     . 
.      .       .     .
2015   12      230   641
2016    1      647    268
2016    2      NA    785
2016    3      NA    419
.      .       .     . 
.      .       .     .
2016   6      NA     369

I'm trying to create a seasonal additive dummy variable that will equal one for December starting in 2014 and continuing on. I can't understand why the following code doesn't work.

SAout <- ifelse(data$Year<= 2014 & data$Month == 12, 1, 0)

For any time after Jan 2016 SAout takes the value NA which makes no sense to me since data$Year is still greater than 2014 .

SAout
[1]  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
 [41]  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
 [81]  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  1  0  0  0  0  0  0  0  0  0  0  0  1  0 NA NA NA NA NA NA

EDIT

I can create the variable I want with the following

data$SAout <- ifelse(data$Year >= 2014 & data$Month == 12, 1, 0)
data$SAout[is.na(data$SAout)]<-0

However I don't understand why the second line of code should be necessary.

Answer 1

Its be because you are trying to create a dummy variable with 2 conditions.

1. data$year > 2013
2. data$month == 12

In your code it says if year and month is equal to 12.

Rather try the following code

data$SAout<-ifelse(data$year >=2014 & data$month==12,1,0)