[R-sig-Geo] Better print method for Spatial*DataFrames?

[Barry Rowlingson]

On Sat, May 29, 2010 at 10:06 AM, Roger Bivand <Roger.Bivand at nhh.no> wrote:


> In other software systems (octave, Stata, ...), one can turn on and off a
> more/less screen-by-screen displayer (not scrolling upwards, just chunking),
> but I'm not aware of an equivalent in R/S. I'm not sure how head() and
> tail() work in R,

 They don't seem to work very well at all for Spatial*DataFrames. If I
add coordinates to meuse to get a SpatialPointsDataFrame and
head(that) I get all the 'rows' but with only the cadmium
measurements. It's slicing it the wrong way. Odd.

> and personally use str() by default. If I need to access
> the coordinates of a particular line or polygon, I print() just that list
> element (Line or Polygon object).
>
> I can see what you mean, but feel that users will benefit much more by using
> str(), which is a real gem!

 str is great if you need to know the str-ucture of an R object. But
it doesn't even align the values so you can see across rows of your
data, which is what I'd like print to do (by analogy with
print.data.frame).

 Currently if I print a SpatialPolygonsDataFrame I get the structure.
Print methods should do better than that - you're almost suggesting
not having, for example, a print method for data frames and that we'd
be better off having what print.default(anyDataFrame) gives us.

 So my proposal is that print of a SpatialPolygonsDataFrame class
should print like a data frame but with some indicator of the geometry
at the start of the row, such as POLYGON(...) - literally with dots,
there's no need to spell it out. Similarly for Lines.

 Another suggestion is for head() and tail methods on
Spatial*DataFrame objects - I think just subscripting [1:n,] from the
object and returning would do it. I think currently head and tail
treat these objects as lists and the results are not pretty.

Barry