# R Notes

## A few very basic R examples

```  myvector = read.csv(file="path_to_csv_file", header=FALSE)
```
• You may then access each of the individual records using myvector[row, column]
• Access entire columns using myvector[,1], myvector[,2], ... myvector[,n]
• Access entire rows using myvector[1,], myvector[2,], ... myvector[n,]

### Scatterplot two columns of a vector

In this example, myvector has 4 columns and we want to plot the 3rd and 4th

```  plot(myvector[,3], myvector[,4], main="This is the title of the plot")
```

### Plot a simple histogram

```  hist(myvector[,3])
```
• Also try plot(density(myvector[,3])) for a density-plot

### Linear regression

```  mymodel = lm(myvector[,3] ~ myvector[,4])
summary(mymodel)
```

### Squeeze multiple plots onto a page ( 4x4 in this example )

```  par(cfrow = c(4,4))
# or par(cfcol = c(4,4)) depending on whether you want row or column ordering
plot(myvector[,3], myvector[,4])
plot(myvector[,3], myvector[,4])
plot(myvector[,3], myvector[,4])
plot(myvector[,3], myvector[,4])
```

### For loops

```  for (i in 1:100) { do_something_useful }
```

## A complete example

• Launch R, and then paste this into the shell:
```  # Scott's quick R example
par (mfrow=c(2,2), oma = c(0, 0, 2, 0), mar = c(5.1, 4.1, 2.1, 2.1));
a = rnorm(1000)
b = rnorm(1000)
c = rlnorm(20000)
d = rnorm(20000, mean=5, sd=20)
plot(a, b, main = "A vs B", xlab="x axis", ylab="y axis", pch=20, col="blue")
plot(c, d, main = "C vs D", xlab="x axis", ylab="y axis", pch=".", col=palette(rainbow(50)))
hist(a, main = "Histogram of A", col="darkgreen")
plot(density(b), main = "Density plot of B", col="red")
mtext("This is an example that combines multiple plots on a single page", line=0.5, outer=TRUE)
```