r - Easy way to convert long to wide format with counts

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Answer 1

The aggregation parameter in the dcast function of the reshape2-package defaults to length (= count). In the data.table-package an improved version of the dcastfunction is implemented. So in your case this would be:

library('reshape2') # or library('data.table')
newdf <- dcast(sample.data, Case ~ Decision)

or with using the parameters explicitly:

newdf <- dcast(sample.data, Case ~ Decision,
               value.var = "Decision", fun.aggregate = length)

This gives the following dataframe:

> newdf
  Case Approved Declined Referred
1    1        1        0        3
2    2        0        1        1
3    3        0        1        2
4    4        1        0        0
5    5        0        1        0

If you don't specify an aggregation function, you get a warning telling you that dcast is using lenght as a default.