gistfile1.r

res <- data.frame(session=NA, dt=NA)

for(event_str in unique(summary$event)) {
  event_name <- gsub(pattern=' ', replacement='.', x=event_str, )
  
  tmp <- summary[ summary$event ==  event_str, c('session', 'dt', 'count')]
  names(tmp)[3] <- event_name
  
  res <- merge(x=res, y=tmp, by=c('session', 'dt'), all=TRUE)
}