spacetime (version 1.2-2)

stConstruct: create ST* objects from long or wide tables

Description

create ST* objects from long or wide tables

Usage

stConstruct(x, space, time, SpatialObj = NULL, TimeObj = NULL, 
	crs = CRS(as.character(NA)), interval, endTime)

Arguments

x

object of class matrix or data.frame, holding the long, space-wide or time-wide table; see details.

space

in case x is a long table, character or integer holding the column index in x where the spatial coordinates are (if length(space)==2) or where the ID of the spatial location is (if (length(space)==1). If x is a space-wide table, a list with each (named) list element a set of columns that together form a variable

time

in case x is a long table, character or integer indicating the column in x with times;

SpatialObj

object of class Spatial-class, containing the locations of a time-wide table, or the locations of a long table

TimeObj

in case of space-wide table, object of class xts, containing the times for each of the columns in a list element of space

crs

object of class CRS-class; only used when coordinates are in x and no CRS can be taken from SpatialObj

interval

logical; specifies whether time should reflect time instance (FALSE) or time intervals (TRUE). If omitted, defaults values depend on the class

endTime

vector of POSIXct, specifying (if present) the end points of observation time intervals

Value

Depending on the arguments, an object of class STIDF or STFDF.

Details

For examples, see below.

A long table is a data.frame with each row holding a single observation in space-time, and particular columns in this table indicate the space (location or location ID) and time.

A space-wide table is a table in which different columns refer to different locations, and each row reflects a particular observation time.

A time-wide table is a table where different times of a particular characteristic are represented as different colunns; rows in the table represent particular locations or location IDs.

References

http://www.jstatsoft.org/v51/i07/

Examples

# NOT RUN {
# example 0: construction of STFDF from long table:
library(maps)
states.m = map('state', plot=FALSE, fill=TRUE)
IDs <- sapply(strsplit(states.m$names, ":"), function(x) x[1])
 
library(maptools)
states = map2SpatialPolygons(states.m, IDs=IDs)

library(plm)
data(Produc)

yrs = 1970:1986
t = as.POSIXct(paste(yrs, "-01-01", sep=""), tz = "GMT")
# deselect District of Columbia, polygon 8, which is not present in Produc:
Produc.st = STFDF(states[-8], t, Produc[(order(Produc[,2], Produc[,1])),])

# example 1: st from long table, with states as Spatial object:
# use Date format for time:
Produc$time = as.Date(paste(yrs, "01", "01", sep = "-"))
# take centroids of states:
xy = coordinates(states[-8])
Produc$x = xy[,1]
Produc$y = xy[,2]
#using stConstruct, use polygon centroids for location:
x = stConstruct(Produc, c("x", "y"), "time", interval = TRUE)
class(x)
stplot(x[,,"unemp"])

# alternatively, pass states as SpatialObj:
Produc$state = gsub("TENNESSE", "TENNESSEE", Produc$state)
Produc$State = gsub("_", " ", tolower(Produc$state))
x = stConstruct(Produc, "State", "time", states[-8])
class(x)
all.equal(x, Produc.st, check.attributes = FALSE)

# stConstruct multivariable, time-wide
library(maptools)
fname = system.file("shapes/sids.shp", package="maptools")[1]
nc = readShapePoly(fname, 
	proj4string = CRS("+proj=longlat +datum=NAD27 +ellps=clrk66"))
timesList = list(
	BIR=c("BIR74", "BIR79"),  # sets of variables that belong together
	NWBIR=c("NWBIR74", "NWBIR79"), # only separated by space
	SID=c("SID74", "SID79")
)
t = as.Date(c("1974-01-01","1979-01-01"))
nc.st = stConstruct(as(nc, "data.frame"), geometry(nc), timesList,
	TimeObj = t, interval = TRUE)

# stConstruct multivariable, space-wide
if (require(gstat)) {
data(wind)
wind.loc$y = as.numeric(char2dms(as.character(wind.loc[["Latitude"]])))
wind.loc$x = as.numeric(char2dms(as.character(wind.loc[["Longitude"]])))
coordinates(wind.loc) = ~x+y
proj4string(wind.loc) = "+proj=longlat +datum=WGS84"

# match station order to names in wide table:
stations = 4:15
wind.loc = wind.loc[match(names(wind[stations]), wind.loc$Code),]
row.names(wind.loc) = wind.loc$Station
# convert to utm zone 29, to be able to do interpolation in
# proper Euclidian (projected) space:

# create time variable
wind$time = ISOdate(wind$year+1900, wind$month, wind$day, 0)

w = STFDF(wind.loc, wind$time, 
	data.frame(values = as.vector(t(wind[stations]))))
space = list(values = names(wind)[stations])
wind.st = stConstruct(wind[stations], space, wind$time, SpatialObj = wind.loc, interval = TRUE)
all.equal(w, wind.st)
class(wind.st)
}
# }