r - Perform operation on subset of factors -

i have factor variable, condition, tells me whether subjects took test or not:

data$condition.f <- factor(data$condition, labels = c("notest", "test")) 

i have variable, x contains right (1) , wrong (0) responses question.

> data$x   [1] na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na na  [42] na na na na na na na na na na na na na na na na na na na na na na na  1  1  1 na na  1  0 na  1  1  1  0  0  0  1  0  1  0  [83]  1  1  0  1 na  1  0  1  1  1  1  1 na  1 na  0  1  1  1  0  1  0  1  1  0 na  1  1  1  1  1  1  0  1 na  1  0  0 

the first half of vector corresponds did not take test (hence nas), , remainder represent did take test.

i replace nas did take test 0. have tried following code:

if (data$condition.f == "test") {         data$x[which(is.na(data$x))] <- 0     } 

but error

warning message: in if (data$condition.f == "test") { :   condition has length > 1 , first element used 

i'm not sure exact issue is, although know has if statement. there better way replace nas 0 took test?

thank you

your problem arises because trying compare vector (data$condition.f) string ("test").

how data$x[is.na(data$x) & data$condition.f == "test"] <- 0 instead?

edit: fixed mistake upon thelatemail's suggestion below.