将自定义函数应用于R中的列

Question

Here is my code, I expect it to insert zero into second place of every column, but it does not work.

insert_zero <- function(smpl_vec){
  return(smpl_vec[2]<-0)
}

my_df = data.frame('col_1'= c(1,2,3), 'col_2'= c(2,3,4))
apply(my_df, 2, insert_zero)

How can I fix it?

PS This is just simplified example. Actual function is more complicated.

Answer 1

You can replace the entire second row with zeros:

my_df[2, ] <- 0 

Be aware that my_df is a data.frame with rows and columns

Answer 2

You're only returning the 2nd value in each column with your current function. This change will make the second value 0 but still return each column in their entirety:

insert_zero <- function(smpl_vec){
  smpl_vec[2] <- 0
  return(smpl_vec)
}

my_df = data.frame('col_1'= c(1,2,3), 'col_2'= c(2,3,4))
apply(my_df, 2, insert_zero)

Answer 3

return(smpl_vec[2]<-0) doesn't return the modified vector

insert_zero <- function(smpl_vec){
  smpl_vec[2]<-0
  return(smpl_vec)
}

Answer 4

Thank you for asking this question. While looking for a solution, I did learn something new. While assigning a new value to cell

 1)  use '<' twice. Below is the statement
 2)  mention the dataframe row and column numbers as mentioned. Below is the modified code

    insert_zero <- function(smpl_vec){
               my_df[2,smpl_vec] <<- 0

            }

          my_df = data.frame('col_1'= c(1,2,3), 'col_2'= c(2,3,4))
          sapply(1:ncol(my_df), function(smpl_vec) insert_zero(smpl_vec))