[R] how to create a pivot table in r?

[peter dalgaard]

There is also

> with(daT, tapply(as.character(ObsDate), list(id, ObsSite), function(x)format(list(x))))
    site1                site4      site5      site7               
id1 NA                   NA         NA         "06/13/13"          
id2 NA                   NA         NA         "07/03/14, 05/17/14"
id4 NA                   "05/08/14" NA         NA                  
id5 NA                   NA         "06/13/14" NA                  
id6 "05/30/14, 06/28/13" NA         NA         NA                  
id7 NA                   NA         "06/25/13" NA     

...with the added bonus that if you leave out the format() business, you get a data structure that doesn't print as nicely, but can be used for further computations:

> with(daT, tapply(as.character(ObsDate), list(id, ObsSite), list, simplify=FALSE))
    site1  site4  site5  site7 
id1 NULL   NULL   NULL   List,1
id2 NULL   NULL   NULL   List,1
id4 NULL   List,1 NULL   NULL  
id5 NULL   NULL   List,1 NULL  
id6 List,1 NULL   NULL   NULL  
id7 NULL   NULL   List,1 NULL  
> M <- with(daT, tapply(as.character(ObsDate), list(id, ObsSite), list, simplify=FALSE))
> M[["id2", "site7"]]
[[1]]
[1] "07/03/14" "05/17/14"

-pd             

> On 6 Feb 2020, at 01:37 , Marna Wagley <marna.wagley using gmail.com> wrote:
> 
> daT<-structure(list(id = structure(c(1L, 2L, 2L, 3L, 4L, 5L, 5L, 6L
> ), .Label = c("id1", "id2", "id4", "id5", "id6", "id7"), class = "factor"),
>    ObsSite = structure(c(4L, 4L, 4L, 2L, 3L, 1L, 1L, 3L), .Label =
> c("site1",
>    "site4", "site5", "site7"), class = "factor"), ObsDate =
> structure(c(4L,
>    8L, 2L, 1L, 5L, 3L, 7L, 6L), .Label = c("05/08/14", "05/17/14",
>    "05/30/14", "06/13/13", "06/13/14", "06/25/13", "06/28/13",
>    "07/03/14"), class = "factor")), .Names = c("id", "ObsSite",
> "ObsDate"), class = "data.frame", row.names = c(NA, -8L))
> daT
> daT$date <- mdy(daT$ObsDate)

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes using cbs.dk  Priv: PDalgd using gmail.com