DataCreation.R

## ------------------------ ##
## Data Creation in R       ##
## Tutorial by Tony Cookson ##
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## Simplest way to create a vector is to use the colon.
a = 1:4
b = 4:1
a
b

## But, they're just sequences
## c() can be useful for creating more interesting
## vectors

y = c(1,2,3,6)  ## basic usage
y2 = c(a,b)     ## binds vectors together into one vector

## More interesting... can create a vector
## recursively

weight = NULL  ## It can be useful to initialize a null vector to define the vector recursively

for(i in 1:14){
 temp= rnorm(10, mean = i*5, sd = 2)
 weight = c(weight, mean(temp))
}

## seq() is a fancy way to create a vector

seq(1, 4)            ## Same as 1:4
seq(0.5, 4)          ## Default Step is 1
seq(1, 4, by = 0.5)  ## Can Go in different number of steps
seq(1, 4, by = 0.4)  ## Doesn't have to partition the interval (1,4)

## It can be useful to repeat a short sequence many times
## The rep() command is useful for this.

x1 = c(1,2,3,1,2,3,1,2,3,1,2,3)  ## 1:3 repeated 4 times
rep(1:3, times = 4)              ## More efficient

x2 = c(1,1,1,1, 2,2,2,2, 3,3,3,3)   ## 1:3 each element repated 4 times
c(rep(1,4), rep(2,4), rep(3,4))     ## Can do it this way
rep(1:3, each = 4)                  ## Or use the "each" option (Most Efficient)

rep(1:3, each = 4, times = 2)

## Can be useful to organize into a matrix

y = rnorm(12, 8, 2)  ## Creates a length 12 vector with a mean of 8 and sd = 2.

## I could also use c() then give the matrix dimensions

x.vec = c(y, x1, x2)
Xalt = matrix(x.vec, ncol = 3)   ## coerces vectors into matrices
Xalt2 = matrix(x.vec, nrow= 12)  ## Equivalent

Xmess = matrix(x.vec, ncol= 3, byrow=TRUE)   ## Can reverse the way the matrix is filled
Xmess = matrix(x.vec, ncol= 12, byrow=TRUE)  ## using byrow

## If I want x1, x2, and y in a matrix,
## I can use cbind() and rbind()

X = cbind(y, x1, x2)
Xrow = rbind(y, x1, x2)

## Maybe I want to use the names, too.
## Then the data.frame() command is useful

Xdf = data.frame(y, x1, x2)
Xdf                 ## The matrix
Xdf$y               ## the vector named y...
                    ## nice to have variable names