A short list of the most useful R commands
A summary of the most important commands with minimal examples. See the relevant part of the guide for better examples. For all of these commands, using the help(function) or ? function is the most useful source of information. Unfortunately, knowing what to ask for help about is the hardest problem.
See the R-reference card by Tom Short for a much more complete list.
Input and display
#read files with labels in first row read.table(filename,header=TRUE) #read a tab or space delimited file read.table(filename,header=TRUE,sep=',') #read csv files x=c(1,2,4,8,16 ) #create a data vector with specified elements y=c(1:10) #create a data vector with elements 1-10 n=10 x1=c(rnorm(n)) #create a n item vector of random normal deviates y1=c(runif(n))+n #create another n item vector that has n added to each random uniform distribution z=rbinom(n,size,prob) #create n samples of size "size" with probability prob from the binomial vect=c(x,y) #combine them into one vector of length 2n mat=cbind(x,y) #combine them into a n x 2 matrix mat[4,2] #display the 4th row and the 2nd column mat[3,] #display the 3rd row mat[,2] #display the 2nd column subset(dataset,logical) #those objects meeting a logical criterion subset(data.df,select=variables,logical) #get those objects from a data frame that meet a criterion data.df[data.df=logical] #yet another way to get a subset x[order(x$B),] #sort a dataframe by the order of the elements in B x[rev(order(x$B)),] #sort the dataframe in reverse order browse.workspace #a menu command that creates a window with information about all variables in the workspace
Moving around
ls() #list the variables in the workspace rm(x) #remove x from the workspace rm(list=ls()) #remove all the variables from the workspace attach(mat) #make the names of the variables in the matrix or data frame available in the workspace detach(mat) #releases the names new=old[,-n] #drop the nth column new=old[n,] #drop the nth row new=subset(old,logical) #select those cases that meet the logical condition complete = subset(data.df,complete.cases(data.df)) #find those cases with no missing values new=old[n1:n2,n3:n4] #select the n1 through n2 rows of variables n3 through n4)
Distributions
beta(a, b) gamma(x) choose(n, k) factorial(x) dnorm(x, mean=0, sd=1, log = FALSE) #normal distribution pnorm(q, mean=0, sd=1, lower.tail = TRUE, log.p = FALSE) qnorm(p, mean=0, sd=1, lower.tail = TRUE, log.p = FALSE) rnorm(n, mean=0, sd=1) dunif(x, min=0, max=1, log = FALSE) #uniform distribution punif(q, min=0, max=1, lower.tail = TRUE, log.p = FALSE) qunif(p, min=0, max=1, lower.tail = TRUE, log.p = FALSE) runif(n, min=0, max=1)
Data manipulation
replace(x, list, values) #remember to assign this to some object i.e., x <- replace(x,x==-9,NA) #similar to the operation x[x==-9] <- NA cut(x, breaks, labels = NULL, include.lowest = FALSE, right = TRUE, dig.lab = 3, ...) x.df=data.frame(x1,x2,x3 ...) #combine different kinds of data into a data frame as.data.frame() is.data.frame() x=as.matrix() scale() #converts a data frame to standardized scores round(x,n) #rounds the values of x to n decimal places ceiling(x) #vector x of smallest integers > x floor(x) #vector x of largest interger < x as.integer(x) #truncates real x to integers (compare to round(x,0) as.integer(x < cutpoint) #vector x of 0 if less than cutpoint, 1 if greater than cutpoint) factor(ifelse(a < cutpoint, "Neg", "Pos")) #is another way to dichotomize and to make a factor for analysis transform(data.df,variable names = some operation) #can be part of a set up for a data set x%in%y #tests each element of x for membership in y y%in%x #tests each element of y for membership in x all(x%in%y) #true if x is a proper subset of y all(x) # for a vector of logical values, are they all true? any(x) #for a vector of logical values, is at least one true?
Statistics and transformations
max() min() mean() median() sum() var() #produces the variance covariance matrix sd() #standard deviation mad() #(median absolute deviation) fivenum() #Tukey fivenumbers min, lowerhinge, median, upper hinge, max table() #frequency counts of entries, ideally the entries are factors(although it works with integers or even reals) scale(data,scale=T) #centers around the mean and scales by the sd) cumsum(x) #cumulative sum, etc. cumprod(x) cummax(x) cummin(x) rev(x) #reverse the order of values in x cor(x,y,use="pair") #correlation matrix for pairwise complete data, use="complete" for complete cases aov(x~y,data=datafile) #where x and y can be matrices aov.ex1 = aov(DV~IV,data=data.ex1) #do the analysis of variance or aov.ex2 = aov(DV~IV1*IV21,data=data.ex2) #do a two way analysis of variance summary(aov.ex1) #show the summary table print(model.tables(aov.ex1,"means"),digits=3) #report the means and the number of subjects/cell boxplot(DV~IV,data=data.ex1) #graphical summary appears in graphics window lm(x~y,data=dataset) #basic linear model where x and y can be matrices (see plot.lm for plotting options) t.test(x,g) pairwise.t.test(x,g) power.anova.test(groups = NULL, n = NULL, between.var = NULL, within.var = NULL, sig.level = 0.05, power = NULL) power.t.test(n = NULL, delta = NULL, sd = 1, sig.level = 0.05, power = NULL, type = c("two.sample", "one.sample", "paired"), alternative = c("two.sided", "one.sided"),strict = FALSE)
More statistics: Regression and Linear model
matrices lm(Y~X1+X2) lm(Y~X|W) solve(A,B) #inverse of A * B - used for linear regression solve(A) #inverse of A factanal() princomp()
Useful additional commands
colSums (x, na.rm = FALSE, dims = 1) rowSums (x, na.rm = FALSE, dims = 1) colMeans(x, na.rm = FALSE, dims = 1) rowMeans(x, na.rm = FALSE, dims = 1) rowsum(x, group, reorder = TRUE, ...) #finds row sums for each level of a grouping variable apply(X, MARGIN, FUN, ...) #applies the function (FUN) to either rows (1) or columns (2) on object X apply(x,1,min) #finds the minimum for each row apply(x,2,max) #finds the maximum for each column col.max(x) #another way to find which column has the maximum value for each row which.min(x) which.max(x) z=apply(big5r,1,which.min) #tells the row with the minimum value for every column
Graphics
par(mfrow=c(nrow,mcol)) #number of rows and columns to graph par(ask=TRUE) #ask for user input before drawing a new graph par(omi=c(0,0,1,0) ) #set the size of the outer margins mtext("some global title",3,outer=TRUE,line=1,cex=1.5) #note that we seem to need to add the global title last #cex = character expansion factor boxplot(x,main="title") #boxplot (box and whiskers) title( "some title") #add a title to the first graph hist() #histogram plot() plot(x,y,xlim=range(-1,1),ylim=range(-1,1),main=title) par(mfrow=c(1,1)) #change the graph window back to one figure symb=c(19,25,3,23) colors=c("black","red","green","blue") charact=c("S","T","N","H") plot(PA,NAF,pch=symb[group],col=colors[group],bg=colors[condit],cex=1.5,main="Postive vs. Negative Affect by Film condition") points(mPA,mNA,pch=symb[condit],cex=4.5,col=colors[condit],bg=colors[condit]) curve() abline(a,b) abline(a, b, untf = FALSE, ...) abline(h=, untf = FALSE, ...) abline(v=, untf = FALSE, ...) abline(coef=, untf = FALSE, ...) abline(reg=, untf = FALSE, ...) identify() plot(eatar,eanta,xlim=range(-1,1),ylim=range(-1,1),main=title) identify(eatar,eanta,labels=labels(energysR[,1]) ) #dynamically puts names on the plots locate() legend() pairs() #SPLOM (scatter plot Matrix) pairs.panels () #SPLOM on lower off diagonal, histograms on diagonal, correlations on diagonal #not standard R, but uses a function found in the psych package matplot () biplot ()) plot(table(x)) #plot the frequencies of levels in x x= recordPlot() #save the current plot device output in the object x replayPlot(x) #replot object x dev.control #various control functions for printing/saving graphic files pdf(height=6, width=6) #create a pdf file for output dev.of() #close the pdf file created with pdf layout(mat) #specify where multiple graphs go on the page #experiment with the magic code from Paul Murrell to do fancy graphic location layout(rbind(c(1, 1, 2, 2, 3, 3), c(0, 4, 4, 5, 5, 0))) for (i in 1:5) { plot(i, type="n") text(1, i, paste("Plot", i), cex=4) }
Distributions
To generate random samples from a variety of distributions
rnorm(n,mean,sd) rbinom(n,size,p) sample(x, size, replace = FALSE, prob = NULL) #samples with or without replacement
Working with Dates
date <-strptime(as.character(date), "%m/%d/%y") #change the date field to a internal form for time #see ?formats and ?POSIXlt as.Date month= months(date) #see also weekdays, Julian
And more…
The psych package has about 300 additional functions that are use for psychological research.
These functions include:
#alpha.scale #find coefficient alpha for a scale and a dataframe of items #describe give means, sd, skew, n, and se #summ.stats #basic summary statistics by a grouping variable #error.crosses #(error bars in two space) #skew find skew #panel.cor taken from the examples for pairs #pairs.panels adapted from panel.cor -- gives a splom, histogram, and correlation matrix #multi.hist #plot multiple histograms #correct.cor #given a correlation matrix and a vector of reliabilities, correct for reliability #fisherz #convert pearson r to fisher z #paired.r #test for difference of dependent correlations #count.pairwise #count the number of good cases when doing pairwise analysis #eigen.loadings #convert eigen vector vectors to factor loadings by unnormalizing them #principal #yet another way to do a principal components analysis -- brute force eignvalue decomp #factor.congruence #find the factor congruence coeffiecints #factor.model #given a factor model, find the correlation matrix #factor.residuals #how well does it fit? #factor.rotate # rotate two columns of a factor matrix by theta (in degrees) #phi2poly #convert a matrix of phi coefficients to polychoric correlations