# $Id: gstat.formula.q,v 1.8 2007-06-08 06:45:52 edzer Exp $
"gstat.formula" <-
function (formula, data)
{
# check for duplicated pixels; if yes coerce to SpatialPointsDataFrame:
if (is(data, "SpatialPixels") && anyDuplicated(data@grid.index) != 0)
gridded(data) = FALSE
m = model.frame(terms(formula), as(data, "data.frame"), na.action = na.fail)
Y = model.extract(m, "response")
if (length(Y) == 0)
stop("no response variable present in formula")
Terms = attr(m, "terms")
X = model.matrix(Terms, m)
has.intercept = attr(Terms, "intercept")
if (gridded(data))
grid = gridparameters(data)
else
grid = numeric(0)
xlevels = .getXlevels(Terms, m)
list(y = Y, locations = coordinates(data), X = X, call = call,
has.intercept = has.intercept, grid = as.double(unlist(grid)),
xlevels = xlevels)
}
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