Creating a New Column to a Data Frame Using a Formula from Another Variable
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...
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.
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