[R-sig-Geo] spacetime: creating STIDF objects

[Facundo Muñoz]

Dear all, I have just posted an issue [1] in the GitHub repository for
the "spacetime" package that I reproduce here:

I have a "long" table with irregular data (observations for some
municipalities at specific months) that I would like to store together
with the administrative map of the region (SpatialPolygons). I tried
unsuccessfully to directly create the STIDF object using both
`stConstruct()` and `STIDF`.

In all the related examples in the package you first create a STFDF
which is later coerced to STIDF. But my dataset is very sparse.

Here is a reproducible example adapted from the examples in the package.
If I use the complete table it leads to a STFDF object as expected and
it works fine. However if the table is not complete it should switch to
a STIDF representation (as far as I understand from the JSS paper).

``` r

library(spacetime)
library(sp)
sp = cbind(x = c(0,0,1), y = c(0,1,1))
row.names(sp) = paste0("point", 1:nrow(sp))
sp = SpatialPoints(sp)
time = as.POSIXct("2010-08-05")+3600*(10:13)
m = c(10,20,30) # means for each of the 3 point locations
mydata = rnorm(length(sp)*length(time),mean=rep(m, 4))

mydata = data.frame(
  space = rep(row.names(sp), 4),
  time  = rep(time, each = 3),
  values = signif(mydata,3)
)

mystfdf <- stConstruct(mydata, "space", "time", sp)  # This works OK

mystidf <- stConstruct(mydata[-1,], "space", "time", sp)
#> Error: nrow(object at time) == length(object at sp) is not TRUE
```


Thank you in advance.

ƒacu.-


[1] https://github.com/edzer/spacetime/issues/30

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*Facundo Muñoz*
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