[R] Advice on Grid Data

[Roger Bivand]

On Fri, 24 Nov 2006, Lorenzo Isella wrote:

> Dear All,
> I would like to automate the analysis and plotting of data taken from a grid.
> Typically I deal with 2 spatial coordinates and a scalar f(x,y), but
> the spatial grid is not evenly spaced at all and usually given in this
> form:
> x                                 y                                     f(x,y)
> 0.0                      0.048979383              2.7659438106975056
> 0.0                      0.044986665              2.603891585041688
> 0.0023807306             0.04787451               2.715949356768243
> 0.0                      0.040993948              2.469223979694342
> 0.0023807306             0.043881793              2.5625191444824265
> 0.004761461              0.046769638              2.6629703119429022
> 0.0                      0.03700123               2.361940994655468
> 0.0023807306             0.039889075              2.436480700580665
> 0.004761461              0.04277692               2.517958884562618
> 0.0071421918             0.045664765              2.606844303834078
> 0.0                      0.060880877              3.470808435449538
> 0.0                      0.05691371               3.1907723461238686
> 0.0020467786             0.059650626              3.3672237912200016
> 0.0                      0.05294655               2.9558174712065237
> 0.0020467786             0.055683464              3.1075221272152054
> 0.004093557              0.05842038               3.268965886866726
> 0.0020467786             0.051716298              2.8929170062920653
> 0.004093557              0.054453213              3.029154848759894
> 0.006140336              0.057190128              3.1754081073235088
> 0.0                      0.02473231               2.138648866573983
> 0.0                      0.020556964              2.092324627395541
> 
> I tried the image plot and lattice but unsuccessfully. Now I am
> reading about the sp package (
> http://cran.r-project.org/src/contrib/Descriptions/sp.html ), but I
> mainly would like a piece of advice about what tools to use and how to
> read and plot these data (I suppose it must be common e.g. in
> geography to deal with this kind of problems).

Your data are not on a 2D grid, there are (here) 7 unique x values, but 21
unique y values of 21. You can treat the data as a SpatialPointsDataFrame
(see note in R News in 2005), but if you want to display them on an actual
grid, you will have to interpolate. For more ideas, perhaps try the 
R-sig-geo mailing list.

> Kind Regards
> 
> Lorenzo
> 
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> and provide commented, minimal, self-contained, reproducible code.
> 

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no