na.strings applied to a dataframe

Question

I currently have a dataframe in which there are several rows I would like converted to \"NA\". When I first imported this dataframe from a .csv, I could use na.strings=c(\"A

Answer 1

Here's a way to replace values in multiple columns:

# an example data frame
dat <- data.frame(x = c("D", "E", "F", "G"), 
                  y = c("A", "B", "C", "D"), 
                  z = c("X", "Y", "Z", "A"))
#   x y z
# 1 D A X
# 2 E B Y
# 3 F C Z
# 4 G D A

# values to replace
na.strings <- c("D", "E", "F")

# index matrix 
idx <- Reduce("|", lapply(na.strings, "==", dat))

# replace values with NA
is.na(dat) <- idx

dat
#     x    y z
# 1     A X
# 2     B Y
# 3     C Z
# 4    G  A