[R] data.frame and ddply

[David Winsemius]

On Apr 16, 2010, at 9:28 AM, arnaud Gaboury wrote:

> Dear group,
>
> Here is my df :
>
>
> futures <-
> structure(list(CONTRAT = c("WHEAT May/10 ", "WHEAT May/10 ",
> "WHEAT May/10 ", "WHEAT May/10 ", "COTTON NO.2 May/10 ", "COTTON NO. 
> 2 May/10
> ",
> "COTTON NO.2 May/10 ", "PLATINUM Jul/10 ", " SUGAR NO.11 May/10 ",
> " SUGAR NO.11 May/10 ", " SUGAR NO.11 May/10 ", " SUGAR NO.11 May/10  
> ",
> " SUGAR NO.11 May/10 ", "ROBUSTA COFFEE (10) May/10 ", "ROBUSTA  
> COFFEE (10)
> May/10 ",
> "ROBUSTA COFFEE (10) May/10 ", "ROBUSTA COFFEE (10) May/10 ",
> "ROBUSTA COFFEE (10) May/10 ", "ROBUSTA COFFEE (10) May/10 ",
> "ROBUSTA COFFEE (10) May/10 ", "ROBUSTA COFFEE (10) May/10 ",
> "ROBUSTA COFFEE (10) May/10 ", "ROBUSTA COFFEE (10) May/10 ",
> "ROBUSTA COFFEE (10) May/10 ", "ROBUSTA COFFEE (10) May/10 "),
>    QUANTITY = c(1, 1, 1, 1, 1, 1, 1, -1, 1, 1, 1, 1, 1, 2, 1,
>    1, 1, 2, 1, 1, 1, 1, 2, 1, 1), SETTLEMENT = c("467.7500",
>    "467.7500", "467.7500", "467.7500", "78.1300", "78.1300",
>    "78.1300", "1,739.4000", "16.5400", "16.5400", "16.5400",
>    "16.5400", "16.5400", "1,353.0000", "1,353.0000", "1,353.0000",
>    "1,353.0000", "1,353.0000", "1,353.0000", "1,353.0000",  
> "1,353.0000",
>    "1,353.0000", "1,353.0000", "1,353.0000", "1,353.0000")), .Names =
> c("CONTRAT",
> "QUANTITY", "SETTLEMENT"), row.names = c(NA, 25L), class =  
> "data.frame")
>
> Here is my code :
>
>> opfut=ddply(futures, c("CONTRAT","SETTLEMENT"), summarise, POSITION=
> sum(QUANTITY))
>
> Here is the output:
>
>> opfut
>                      CONTRAT SETTLEMENT POSITION
> 1         SUGAR NO.11 May/10     16.5400        5
> 2         COTTON NO.2 May/10     78.1300        3
> 3            PLATINUM Jul/10  1,739.4000       -1
> 4 ROBUSTA COFFEE (10) May/10  1,353.0000       15
> 5               WHEAT May/10    467.7500        4
>
> It is almost exactly what I want, except I am expecting the POSITION  
> column
> before the SETTLEMENT column. How can I modified my code to obtain  
> this?

Most compact way:
opfut[, c(1,3,2)]

Better readability:
opfut[, c("CONTRAT", "POSITION", "SETTLEMENT")]

And that particular operation is really basic stuff, suggesting that  
you should go back to the basic R documents and spend some more time  
educating yourself. Either of those extract operations could have been  
appended on the ddply call as well, e.g.:

  opfut=ddply(futures, c("CONTRAT","SETTLEMENT"), summarise, POSITION=  
sum(QUANTITY))[, c(1,3,2)]
  opfut
#----------------
                        CONTRAT POSITION SETTLEMENT
1          SUGAR NO.11 May/10         5    16.5400
2         COTTON NO.2 May/10\n        1    78.1300
3          COTTON NO.2 May/10         2    78.1300
4             PLATINUM Jul/10        -1 1,739.4000
5 ROBUSTA COFFEE (10)\nMay/10         1 1,353.0000
6  ROBUSTA COFFEE (10) May/10        14 1,353.0000
7                WHEAT May/10         4   467.7500

("Functional programming")


-- 

David Winsemius, MD
West Hartford, CT