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Really simple question, to which I haven't been able to Google/find an answer.

I have a simple file - "test.txt"

Gender arch1
M      99
F      97
M      NA

I load this into a resultset using read.table - works fine.

attach(resultset)

Now, I want _something_ that will give me

mean(arch1, [_SOMETHING_]) = 65.3 (and *_NOT_* 98)

i.e. not na.rm = T or similar. Basically, I want to treat NA as 0 - and I don't want to do something complicated like here with matrices and dataframes.

Just NA = 0 from the file. Surely, I can't be the first person to have wanted this? And I don't want discussions about how NA and 0 are not the same thing. I think it's perfectly valid to want to calculate an average even over missing students!

Vérace
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4 Answers4

6

Something like this?

sum(arch1, na.rm = T)/length(arch1)
JACKY88
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  • Why "sum" - I asked for a mean? I think I'm right in saying that sum(arch1, na.rm = T) will be the equivalent of summing arch1 with NA = 0 anyway? – Vérace Dec 08 '18 at 21:41
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    The `na.rm = TRUE` is so the function doesn't return NA. Dividing by the length gives the mean. – mickey Dec 08 '18 at 21:47
5

You can replace the NAs with zeros before using mean:

mean(replace(arch1, is.na(arch1), 0))
# [1] 65.33333
Sven Hohenstein
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0

you could replace the NA by zero with resultset$arch1[is.na(resultset$arch1)]=0 and then compute the mean of the arch1 column

David Cros
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  • > resultset$arch1[is.na(resultset$arch1)]=0 Error in `$<-.data.frame`(`*tmp*`, arch1, value = numeric(0)) : replacement has 0 rows, data has 9 > – Vérace Dec 08 '18 at 21:43
-1

Below is my suggestion on how to implement the solution to which I have now given as the correct answer:

avg_without_NA = function(vec) 
{
  my_ans = sum(vec, na.rm = T)/length(vec)
  return(my_ans)
}

So, now all I have to do is make a simple function call and my code is encapsulated in! Simpler all round, and easier to read!

Vérace
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