根据其他列数据框r中的值添加列

Question

I'm curious about how to solve this problem. I have data frame like this:

a    b    
1    0    
1    0
0    1
1    1
0    0
1    0   

Then the output has an extra column based on values of "a" and "b":

if(a==1&b==1) c=1, if(a==1&b==0) c=2, if(a==0&b==1) c=3, else c=4.

a    b    c
1    0    2
1    0    2
0    1    3
1    1    1
0    0    4
1    0    2

Any thoughts? I don't to write a for loop with nested if-else, how could we go vectorize? Thanks!

Answer 1

interaction is made for this:

c(4,2,3,1)[interaction(df)]
#[1] 2 2 3 1 4 2

Answer 2

This will also work:

library(dplyr)
inner_join (df, cbind(expand.grid(0:1, 0:1), c=c(4, 2, 3, 1)), 
                by=c('a'='Var1', 'b'='Var2'))

  a b c
1 1 0 2
2 1 0 2
3 0 1 3
4 1 1 1
5 0 0 4
6 1 0 2

Answer 3

With a little bit of linear algebra:

we need to solve for x,y from the equation c = 4 - x a - y b we can see x = 2, y = 1 is the solution given the set of variable values

 a  b c
 0  0 4
 1  0 2
 0  1 3
 1  1 1

or we can use the limSolve to solve this over-determined set of equations:

library(limSolve)
res <- Solve(as.matrix(expand.grid(0:1, 0:1)), 4-c(4, 2, 3, 1))
res
Var1 Var2  # a = Var1, b = Var2
   2    1

Hence, we have:

df$c <- 4 - res[1]*df$a - res[2]*df$b
df
a b c
1 1 0 2
2 1 0 2
3 0 1 3
4 1 1 1
5 0 0 4
6 1 0 2

Answer 4

Map your desired c-values to a vector and use a and b values as indices (increment by 1 for 1-based indexing).

foo <- data.frame(a=c(1,1,0,1,0,1), b=c(0,0,1,1,0,0))

data.frame(foo, c=c(4:1)[foo$a*2 + foo$b + 1])

#   a b c
# 1 1 0 2
# 2 1 0 2
# 3 0 1 3
# 4 1 1 1
# 5 0 0 4
# 6 1 0 2