[R] Counting observations split by a factor when there are NAs in the data

From: Jenifer Larson-Hall <jenifer_at_unt.edu>
Date: Tue 11 Jul 2006 - 05:24:12 EST

I am a very novice R user, a social scientist (linguist) who is trying to learn to use R after being very familiar with SPSS. Please be kind!

My concern:
I cannot figure out a way to get an accurate count of observations of one column of data split by a factor when there are NAs in the data.

I know how to use commands like tapply and summaryBy to obtain other summary statistics I am interested in, such as the following: tapply(RLWTEST, list(STATUS), mean, na.rm=T) summaryBy(RLWTEST~STATUS, data=lh.forgotten, FUN=c(mean, sd, min, max), na.rm=T)

However, with tapply I know I cannot use length to get a count where there are NAs. summaryBy appears to work the same way. I do know how to get a count of the entire column using sum: sum(!is.na(lh.forgotten$RLWTEST))

However, this does not give me a count split up by my factor (STATUS). I have looked through Daalgard (2002) and Verzani (2005), and have searched the help files, but with no luck.

Thank you in advance for your help. I love R and am interested in making it more accessible to social scientist types like me. I know it can do everything SPSS can and more, but sometimes the very simplest things seem to be a lot harder in R.


Dr. Jenifer Larson-Hall
Assistant Professor of Linguistics
University of North Texas

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