Question

I am trying to apply different functions to different rows based on the value of a string in an adjacent column. My dataframe looks like this:

type    size
A       1
B       3
A       4
C       2
C       5
A       4
B       32
C       3

and I want to apply different functions to types A, B, and C, to give a third column column “size2.” For example, let’s say the following functions apply to A, B, and C:

for A: size2 = 3*size
for B: size2 = size
for C: size2 = 2*size 

I’m able to do this for each type separately using this code

df$size2 <- ifelse(df$type == "A", 3*df$size, NA)
df$size2 <- ifelse(df$type == "B", 1*df$size, NA)
df$size2 <- ifelse(df$type == "C", 2*df$size, NA)

However, I can’t seem to do it for all of the types without erasing all of the other values. I tried to use this code to limit the application of the function to only those values that were NA (i.e., keep existing values and only fill in NA values), but it didn’t work using this code:

df$size2 <- ifelse(is.na(df$size2), ifelse(df$type == "C", 2*df$size, NA), NA)

Does anyone have any ideas? Is it possible to use some kind of AND statement with “is.na(df$size2)” and “ifelse(df$type == “C””?

Many thanks!

Answer 1

if you want you can nest the ifelses:

df$size2 <- ifelse(df$type == "A", 3*df$size,
                       ifelse(df$type == "B", 1*df$size,
                           ifelse(df$type == "C", 2*df$size, NA)))


#    > df
#  type size size2
#1    A    1     3
#2    B    3     3
#3    A    4    12
#4    C    2     4
#5    C    5    10
#6    A    4    12
#7    B   32    32
#8    C    3     6