How to select the rows of a dataframe where two variables have value

Question

So I have a dataframe: df1. And I want to select the rows based on the value of two variables != NULL.

For example:

Variable1    Variable2

NULL         5

6            NULL

NULL         NULL

3            6

1            9

Result:

Variable1   Variable2

3            6

1            9

Answer 1

df1 <- data.frame(Variable1 = c("NULL", 6, "NULL", 3, 1), Variable2 = c(5, "NULL", "NULL", 6, 9))
df1 <- df1[df1$Variable1 != "NULL" & df1$Variable2 != "NULL",]