How to make a cross table with NA instead of X?

Question

I have the following dataset (see for loading dataset below)

     ID       Date qty
1  ID25 2007-12-01  45
2  ID25 2008-01-01  26
3  ID25 2008-02-01  46
4  ID25 2008-03-01   0
5  ID25 2008-04-01  78
6  ID25 2008-05-01  65
7  ID25 2008-06-01  32
8  ID99 2008-02-01  99
9  ID99 2008-03-01   0
10 ID99 2008-04-01  99

And I would like to create a pivot table of that. I do that with the following command and that seems to be working fine:

pivottable <- xtabs(qty ~ ID + Date, table)

The output is the following:

ID     2007-12-01 2008-01-01 2008-02-01 2008-03-01 2008-04-01 2008-05-01 2008-06-01
ID25         45         26         46          0         78         65         32
ID99          0          0         99          0         99          0          0

However, for ID99 there are only values for 3 periods the rest is marked as '0'. I would like to display NA in the fields that have no values in the first table. I would like to get a table that looks as following:

ID     2007-12-01 2008-01-01 2008-02-01 2008-03-01 2008-04-01 2008-05-01 2008-06-01
ID25         45         26         46          0         78         65         32
ID99         NA         NA         99          0         99         NA         NA

Any suggestion on how to accomplish this?

Loading dataset:

table <- structure(list(ID = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 
2L, 2L), .Label = c("ID25", "ID99"), class = "factor"), Date = structure(c(7L, 
1L, 2L, 3L, 4L, 5L, 6L, 2L, 3L, 4L), .Label = c("01/01/2008", 
"01/02/2008", "01/03/2008", "01/04/2008", "01/05/2008", "01/06/2008", 
"01/12/2007"), class = "factor"), qty = c(45L, 26L, 46L, 0L, 
78L, 65L, 32L, 99L, 0L, 99L)), .Names = c("ID", "Date", "qty"
), class = "data.frame", row.names = c(NA, -10L))

table$Date <- as.POSIXct(table$Date, format='%d/%m/%Y')

Answer 1

You could use xtabs twice to obtain the output you are looking for:

1. Create the table:

    pivottable <- xtabs(qty ~ ID + Date, table) 

2. Replace all zeros of non-existing combinations with NA :

    pivottable[!xtabs( ~ ID + Date, table)] <- NA 

The output:

      Date
ID     2007-12-01 2008-01-01 2008-02-01 2008-03-01 2008-04-01 2008-05-01 2008-06-01
  ID25         45         26         46          0         78         65         32
  ID99                               99          0         99                      

Note that NA s are not displayed. This is due to the print function for this class. But you could use unclass(pivottable) to achieve regular behavior of print .