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general commands

[]: 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
- 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