[R] replacing <NA> in character column

[David Winsemius]

On Oct 28, 2009, at 5:19 PM, Mark Miller wrote:

> I have a small Excel data file with two columns of character  
> variables, one column with a numeric variable and three rows.  One  
> of the character cells is blank and one of the numeric cells is blank.
>
> I read the data file with the following code:
>
>
> library(RODBC)
>
> channel <- odbcConnectExcel('u:/test.xls')
> sqlTables(channel)
>
> s1 <- sqlFetch(channel, "Sheet1")
>
> odbcClose(channel)
>
> s1
>
>
>
> The code prints the data file as:
>
>  Firstname  Lastname Age
> 1    Bob       Smith   20
> 2   John       Clark   NA
> 3   Andy       <NA>    40

I am guessing that your <NA> is not really an NA_character,  but  
rather a factor with a level of "<NA>".

See if str(s1) confirms my suspicions.

 > df1 <- read.table(textConnection(" Firstname  Lastname Age
+ 1    Bob       Smith   20
+ 2   John       Clark   NA
+ 3   Andy       <NA>    40"), header=T)
 > levels(df1$Lastname)
[1] "<NA>"  "Clark" "Smith"
 > levels(df1$Lastname)[1] <- "qqqq"
 > levels(df1$Lastname)
[1] "qqqq"  "Clark" "Smith"
 > df1
   Firstname Lastname Age
1       Bob    Smith  20
2      John    Clark  NA
3      Andy     qqqq  40


>
>
> I can replace the NA with the number zero in the second row of the  
> third (‘Age’) column using the following line:
>
> s1[is.na(s1[,3]), 3] <- 0
>
>
> What code can I use to replace the <NA> in the third row of the  
> second (‘Lastname’) column with qqqqqqqq?
>
> Thank you in advance for any advice.
>

-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT