Question

It seems like such a simple problem, yet i’ve been pulling my hair out trying to get this to work:

Given this data frame identifying the interactions idhad with contact who is grouped by contactGrp,

head(data)
   id               sesTs  contact    contactGrp   relpos   maxpos
1 6849 2012-06-25 15:58:34   peter        west    0.000000      3
2 6849 2012-06-25 18:24:49   sarah        south   0.500000      3
3 6849 2012-06-27 00:13:30   sarah        south   1.000000      3
4 1235 2012-06-29 17:49:35   peter        west    0.000000      2
5 1235 2012-06-29 23:56:35   peter        west    1.000000      2
6 5893 2012-06-30 22:21:33   carl         east    0.000000      1

how many contacts where there for unique(data$contactGrp) with relpos=1 and maxpos>1 ?

An expected Result would be:

1 west   1
2 south  1
3 east   0

A small subset of lines i have tried:

• aggregate(data, by=list('contactGrp'), FUN=count) yields an error, no filtering
• using data.table seems to require a key, which is not unique in this data…
• ddply(data,"contactGrp",summarise,count=???) not sure which function to use to fill the count column
• ddply(subset(data,maxpos>1 & relpos==0), c('contactGrp'), function(df)count(df$relpos)) works but gives me an extra column x and it feels like i’ve overcomplicated it…

SQL would be easy: Select contactGrp, count(*) as cnt from data where … Group by contactGrp but im trying to learn R

Answer 1

I think this is the ddply version you’re looking for:

ddply(sessions,.(contactGrp),
      summarise,
      count = length(contact[relpos == 0 & maxpos > 1]))