R/db.R

In faridcher/futils: Farid utility functions

# PL/R
#
#
# settlements = readOGR(Datadir,”settlements.shp”)
# slayer = layer(spTransform(settlements,
#                            CRS('+init=epsg:4326')),
#                'settlements')
# mway = readOGR(Datadir,”mways.shp”)
# mlayer = layer(spTransform(mway,
#                            CRS(”+init=epsg:4326”)),
#                ”Motorways”)
# osmMap(slayer,mlayer,title=”Towns and Roads”)
#
# Client: either RpgSQL or rgdal
# Server: PL/R
# Managing big data sets
# Spatial queries
#
# RPostgreSQL (better than Rpgsql):
#   con = dbConnect(dbDriver('PostgreSQL'),
#                   user='gis',dbname='maps')
# rs = dbSendQuery(con,
#                  'select * from countries where pop > 1000000')
# countries = fetch(rs,-1)
#
# PL/R
# SELECT town, mean(age) AS m FROM people
# GROUP BY town ORDER BY m;
# No 'median' function in SQL- so we'll make one...
# CREATE function r_median(_float8)
# RETURNS FLOAT AS 'median(arg1)' LANGUAGE 'plr';
# CREATE AGGREGATE median (
# sfunc = plr_array_accum,
# basetype = float8,
# stype = _float8,
# finalfunc = r_median
# );
# SELECT town, median(age) AS m FROM people
# GROUP BY town ORDER BY m;