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some useful functions

To use a function below, copy and paste the corresponding line in black (starts with 'source') into R. This will load the function into R and will make it available for use. Follow the directions that accompany a function for how to use it.

# normal curve

# normal curve

# add.normal is a function to add a normal curve to an 
# existing histogram made with 'hist'. the function is
# explicitly written out below in the R language:
add.normal <- function(data, color="blue"){
    R <- range(data)
    M <- mean(data)
    SD <- sd(data)
  #==> setting up an vector over the domain <==#
  #==> change the 200 to a larger number for more curve detail <==#
    x <- seq(R[1]-SD, R[2]+SD, length.out=200)
  #==> finding the normal density over x <==#
    y <- dnorm(x, M, SD)
  #==> plotting the points <==#
    points(x, y, type="l", col=color)

# function rule: the input for the function must be a numerical data vector

# below is an example of how to use this function:
# download and attach the data
bumpus <- read.delim("http://www.stat.ucla.edu/~david/Bumpus.txt", header=T)
# the next two lines of code create a histogram and then plot the normal curve
# to one of the numerical columns of bumpus:
hist(Length_mm[Survival], freq=F) # it is crucial to have 'freq=F' in hist

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