[gov2001-l] NA and TRUE

Hi Olivia, I need to send you an email copy of the memo (the homework), could you please let me know your email address? I am not sure whether I could send it to you by this email account. Thanks. Chunling -----Original Message----- From: gov2001-l-bounces(a)lists.fas.harvard.edu [mailto:gov2001-l-bounces@lists.fas.harvard.edu]On Behalf Of Olivia Lau Sent: Sunday, November 21, 2004 4:46 PM To: gov2001-l(a)lists.fas.harvard.edu Subject: Re: [gov2001-l] NA and TRUE The key thing to understand here is that R treats an NA as a missing value -- literally. Which means that if you want to do a logical operation on a NA value, you get "missing value where TRUE/FALSE needed". Since R doesn't know what to do if the logical value is missing, and so keeps the row by default. You need to omit the NA values using: nrow(na.omit(data[data$var,])) This has the effect of omitting observations 3-5 below: x y 1 TRUE 1 2 TRUE 2 3 TRUE NA 4 FALSE 3 5 NA 4 That is, if any of the variables for which x is TRUE has an NA in any of of the *other* variables, that row will be omitted from the count. Also, note that data$var == TRUE is redundant in this case, and also note that you should use the name of the variable, not a column indicator. (You want to preserve the indexing of observations against each other.) Also, Allan's hack from yesterday works too... Olivia. On Sat, 20 Nov 2004, Andrew Eggers wrote: _______________________________________________ gov2001-l mailing list gov2001-l(a)lists.fas.harvard.edu http://lists.fas.harvard.edu/mailman/listinfo/gov2001-l