general commands

install.packages(“packageName”): download and install a package –> start R as following: Rgui.exe –internet2
help(package=XML): information about the package XML
str(a): display the structure of a object
table(x): returns a table with the numbers of the different values of x
[]: subscript a string
as.matrix.data.frame(data): convert data to a matrix
image.plot(x, y, matrix): color matrix (library(filds))
attach, detach: open/close table
read.table(…):
- skip=n: begin to read rows after n rows
- row.names=n: the row names are in column n or a vector giving the actual row names
- nrows=n: read maximal n rows
- fill=TRUE: show missing values
- na.strings=“N.A.”: transform N.A. in NA (missing values)
for(i in 1:ncol(data)) if(is.numeric(data[,i])) data[is.na(data[,i]),i] ← 0: transform all NA to 0
object ← cbind(object, as.matrix(“newColumn”)): add new column or row(rbind) to an existing matrix
byrow=TRUE (in matrix): makes the matrix row by row (instead of column by column)
legend.lab: write a legend in image.plot
- better way: legend.args=list( text=“legend text”, cex=1.0, side=4, line=2)

dimnames(matrix) ← list(row names, col names): name rows and columns in a matrix
las: rotation of text margins
par(…): can be used to set or query graphical parameters
- mar: A numerical vector of the form c(bottom, left, top, right) which gives the number of lines of margin to be specified on the four sides of the plot. The default is c(5, 4, 4, 2) + 0.1.
- mfcol, mfrow: A vector of the form c(nr, nc). Subsequent figures will be drawn in an nr-by-nc array on the device by columns (mfcol), or rows (mfrow), respectively. Consider the alternatives, layout and split.screen.
- mfg: A numerical vector of the form c(i, j) where i and j indicate which figure in an array of figures is to be drawn next (if setting) or is being drawn (if enquiring). The array must already have been set by mfcol or mfrow.