I want to create a new column to a data frame using a formula from another variable.
Example:
I have a data set "aa" is;
x y 2 3 4 5 6 7 My R code is;
>bb <- "x+y-2" >attach(aa) >aa$z<- bb >detach(aa) the result is;
x y z 2 3 x+y-2 4 5 x+y-2 6 7 x+y-2 but I want like this;
x y z 2 3 3 4 5 7 6 7 11 Could you please help me..
3 Answers
If you want to evaluate an expression in the context, of a data frame, you can use with and within.
aa$z <- with(aa, x + y - 2) or
aa <- within(aa, z <- x + y - 2) Or, if your expression is in the form of a text string (you should see if there are other ways to write your code; evaluating arbitrary text strings can lead to lots of problems):
aa$z <- eval(parse(text="x + y - 2"), aa) You should probably read some basic tutorials on R other than An Introduction to R as despite what is written there the $ notation is more sensible and easier to understand than attach/detach. Try this in the meantime.
aa <- data.frame(x = c(2, 4, 6), y = c(3, 5, 7)) Which gives:
> aa x y 1 2 3 2 4 5 3 6 7 Then enter:
aa$z <- (aa$x + aa$y) - 2 Which gives:
> aa x y z 1 2 3 3 2 4 5 7 3 6 7 11 you can use mutate from the package dplyr
library(dplyr) aa <- aa %>% mutate(z = x+y-2) Hope it helps.
