Ignoring NA values in function

问题

Im writing my own function to calculate the mean of a column in a data set and then applying it using apply() but it only returns the first columns mean. Below is my code

mymean <- function(cleaned_us){
  column_total = sum(cleaned_us)
  column_length = length(cleaned_us)
  return (column_total/column_length)
}

Average_2 <- apply(numeric_clean_usnews,2,mymean,na.rm=T)

回答1:

We need to use the na.rm=TRUE in the sum and using it in apply is not going to work as mymean doesn't have that argument

mymean <- function(cleaned_us){
   column_total = sum(cleaned_us, na.rm = TRUE) #change
   column_length = sum(!is.na(cleaned_us)) #change
  return(column_total/column_length)
 }

Note that colMeans can be used for getting the mean for each column.

回答2:

In order to pass an na.rm parameter to the function you defined, you need to make it a parameter of the function. The sum() function has an na.rm param, but length() doesn't. So to write the function you are trying to write, you could say:

# include `na.rm` as a param of the argument 
mymean <- function(cleaned_us, na.rm){

  # pass it to `sum()` 
  column_total = sum(cleaned_us, na.rm=na.rm)

  # if `na.rm` is set to `TRUE`, then don't count `NA`s 
  if (na.rm==TRUE){
    column_length = length(cleaned_us[!is.na(cleaned_us)])

  # but if it's `FALSE`, just use the full length
  } else {
    column_length = length(cleaned_us)
  }

  return (column_total/column_length)
}

Then your call should work:

Average_2 <- apply(numeric_clean_usnews, 2, mymean, na.rm=TRUE)

回答3:

Use na.omit()

set.seed(1)
m <- matrix(sample(c(1:9, NA), 100, replace=TRUE), 10)

mymean <- function(cleaned_us, na.rm){
    if (na.rm) cleaned_us <- na.omit(cleaned_us)
    column_total = sum(cleaned_us)
    column_length = length(cleaned_us)
    column_total/column_length
}

apply(m, 2, mymean, na.rm=TRUE)

# [1] 5.000 5.444 4.111 5.700 6.500 4.600 5.000 6.222 4.700 6.200

来源：https://stackoverflow.com/questions/47241761/ignoring-na-values-in-function

标签

function