R - Replace specific value contents with NA [duplicate]

Answer 1

I believe the simplest solution is with base R function is.na<-. It's meant to solve precisely that issue.

First, make up some data. Then set the required values to NA.

set.seed(247)    # make the results reproducible

df <- data.frame(X = 1:10, Y = sample(c("-", letters[1:2]), 10, TRUE))

is.na(df) <- df == "-"
df
#    X    Y
#1   1    a
#2   2    b
#3   3    b
#4   4    a
#5   5 
#6   6    b
#7   7    a
#8   8 
#9   9    b
#10 10    a