在数据表 R 中，如何创建一个新变量，该变量为特定观察值取特定值？

Question

In data table, i am trying to make a variable that takes a value when a certain observation has been met.

smoked <- matrix(c("A","A","A","B","B","B","A","B","A"),ncol=3,byrow=TRUE)
colnames(smoked) <- c("Type","Name","cusip")
rownames(smoked) <- c("A","B","C")
smoked <- as.table(smoked)
smoked

How would i create a another column that that responds "B" every occasion the condition is met within the "name" columnn.. and then "not B" for every occasion it does not.

Answer 1

Try using cbind() with the ifelse() function.

smoked <- matrix(c("A","A","A","B","B","B","A","B","A"),ncol=3,byrow=TRUE)
colnames(smoked) <- c("Type","Name","cusip")
rownames(smoked) <- c("A","B","C")
smoked <- as.table(smoked)

# use cbind
smokedNew <- cbind(smoked, newCol = ifelse(test = smoked[,"Name"] == "B", yes = "B", no = "not B"))

smokedNew

#   Type Name cusip newCol 
# A "A"  "A"  "A"   "not B"
# B "B"  "B"  "B"   "B"    
# C "A"  "B"  "A"   "B"  

Answer 2

If the data comes as data frame, it is straight forward:

#create data frame
smoked <- data.frame( Type=c("A","B","A"), Name=c("A","B","B"), cusip=c("A","B","A"))

# test function
my.test <- function(test.value, test.on) { paste0(ifelse(test.value==test.on,'','not '), test.on) }

# now testing on content of Name colum
smoked$res1 <- sapply( smoked$Name, FUN=my.test, test.on='B' )
smoked$res2 <- sapply( smoked$Name, FUN=my.test, test.on='C' )

which yields:

> print(smoked)
  Type Name cusip  res1  res2
1    A    A     A not B not C
2    B    B     B     B not C
3    A    B     A     B not C