R tips must know by Geospatial Analyst

1) Merge ESRI shape file with external CSV or data frame to plot the map with CSV/data frame variables

library(maptools)

library(sp)

library(shapefiles)

library(RColorBrewer)    # creates nice color schemes

library(classInt)               # finds class intervals for continuous variables

#Read files

csvvalues=read.csv(“c:/csv_path ")

shapefile= readShapePoly("c:/shape.shp")

#Merge data by unique ID

shapefile@data <-data.frame(shapefile@data, csvvalues, by="ID")

attach(shapefile@data)

# Define the number of classes to be mapped

nclass <- 5

# Set the color ramp that will be used to plot these classes

cols <- brewer.pal(nclass,"YlGnBu")

# Set the class breakpoints using equal intervals

# Can also use quantiles or natural breaks - see help(classIntervals)

breaks <- classIntervals(Column_name_to_be_mapped, nclass, style="quantile")

# Based on the breakpoints and color ramp, specify a color to plot for each polygon

plotcols <- findColours(breaks, cols)

# Generate the map

plot (shapefile, col=plotcols)

Reference:  http://geography.uoregon.edu/geogr/topics/maps.htm

2) Combine multiple data frames with similar names into a single data frame using matched column names.
Ex. Use gtools library and smart bind function.
library (“gtools”)
df_result <- smartbind(df1,df2)



3) List files recursively inside directory tree.
Ex. List all *.txt files inside directory tree
fileList=list.files(path= “file Location”,pattern="txt$",all.files=TRUE,full.names=TRUE,recursive=TRUE)
Try to play with grep() if you need more specific filter based on file names not by files types only.

4) List all files in home directory

 setwd(homeDir)
 home_files_list<-list.files(pattern="*.txt")
        or
 home_files_list<-list.files()


5) Replace NA by 0
Ex. X[is.na(X[])]<-0


6) Exclude/Remove  columns from data frame
Ex: Select only matched columns
X[, colnames(X) != c('col1','col2')]
X[, colnames(X) != ‘col3’

R