count NAs per week

with(dattrial, table(A_is_missing=is.na(a), Week))
Week
A_is_missing 3 4
       FALSE 2 3
       TRUE  1 0
with(dattrial, table(A_is_missing=is.na(a), Week))["TRUE", ] # extract the missing="TRUE" row, note quotes
3 4 
1 0

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
Of Tagmarie
Sent: Monday, September 17, 2012 3:03 AM
To: r-help at r-project.org
Subject: [R] count NAs per week

Even though I work with R since a year or so I still struggle with simple
problems. I hope someone can help me with this. Been trying for days and am
a little frustrated now.

I have a data frame somewhat like the one bellow:

dattrial<-data.frame(a=c(1,NA,rnorm(4,10)), Week=c(3,3,3,4,4,4))

I want to know how many NAs I have in week 3 and in week 4.

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count NAs per week

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