How to apply a function on a specific column in the data frame using R?

Question

R newbie is here, and I'm tying to figure out how to apply a function on every row in a data frame and add the result to the data frame. To be more precise, I'm providing an example below.

So say I have:

n = c(2, 3, 5) 
s = c("aa", "bb", "cc") 
b = c(TRUE, FALSE, TRUE) 
df = data.frame(n, s, b)
df

   n  s     b
1  2 aa  TRUE
2  3 bb FALSE
3  5 cc  TRUE

my dummy function is:

dummyfunc <- function(x)
{  
  return (x*2)
}

my goal is to apply dummyfunc on the column n and to get the following result:

   n   s     b
1  4  aa  TRUE
2  6  bb FALSE
3  10 cc  TRUE

I learned that apply can do that but I couldn't figure it out how to use it on each row.

Answer 1

您不需要套用，只需运行df$n <- dummyfunc(df$n) 。

Answer 2

You can use transform

> (df2 <- transform(df, n=dummyfunc(n)))
   n  s     b
1  4 aa  TRUE
2  6 bb FALSE
3 10 cc  TRUE

within is also valid

> (df3 <- within(df, n <- dummyfunc(n)))

Answer 3

to answer your question on using apply, try this

df <-apply(df["n"],1, function(x) x *2)

The 1 is the value given to margin, read ?apply for more details. the 1 is telling apply to "apply" the function to each row. if instead you wanted to apply it to columns, you would use 2.

though I suggest using transform() (as suggested above), as it is better suited for working with data.frames just remember to assign the result of transform() back to df or another data.frame