[R] how to handle missing values "." when importing data in

[(Ted Harding)]

On 12-Jan-10 17:46:47, karena wrote:
> hi, I have a question about importing data in R.
> 
> I want to import a file which has missing value in it, and the missing
> values are denoted as ".", I want to first read in the file, and then
> change the "." into the number zero "0".
> 
> how can I do that?
> 
> thank you,
> 
> karena

It may depend on what format the file is in, but if it is a tabular
text file or a CSV file then you can use the "na.strings" parameter.
Here is an example of a little CSV file with "." used for "missing":

file temp.csv:
--------------
A,B,C,D
1.1,1.2,1.3,1.4
2.1,2.2,.,2.4
3.1,.,3.3,3.4
4.1,.,.,4.4

  D <- read.csv("temp.csv",na.strings=".")
  D
  #     A   B   C   D
  # 1 1.1 1.2 1.3 1.4
  # 2 2.1 2.2  NA 2.4
  # 3 3.1  NA 3.3 3.4
  # 4 4.1  NA  NA 4.4

So the "." have gone in as NA (the right thing to do in the first
instance with missing data). Now you can replace these by zeros:

  D[is.na(D)] <- 0
  D
  # 1 1.1 1.2 1.3 1.4
  # 2 2.1 2.2 0.0 2.4
  # 3 3.1 0.0 3.3 3.4
  # 4 4.1 0.0 0.0 4.4

Ted.

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Date: 12-Jan-10                                       Time: 18:42:40
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