data.frame in R (the key object)

I've been wading through R trying to figure out how it all works. It looks like the most important data structure is the data frame, and here I demo how to make a dataframe that a person can then play with. Yes, you can import data from a spreadsheet, but a person should understand the underlying data structure.

A data.frame is just a list of vectors or matrices where each has the same number of rows (think of the vectors as columns). It really is just the same as data in a spreadsheet:

var1	var2	var3	fac1	fac2
1	3	4	hot	TX
0	2	3	cold	WI
3	8	2	cold	UT

In fact, when one reads in this type of info, one gets a data.frame back:

df = read.csv(".csv", quote="")  # <-reads an unquoted csv file with headers

So, assuming we have some data like the above, now lets make it in R:

> var1 <- c(1,0,3)    #  '<-' is the assignment operator (like a directional '=')
                      #  'c()' is the concatenate operator (makes lists of things)
> var2 <- c(3,2,8)
> var3 <- array( c(4,3,2), c(3) )  # here's how you make a more mathematical vector

> fac1 <- c("hot", "cold", "cold")
> fac2 <- c("TX","WI","UT")

# alright, lets add all this stuff together into a dataframe:

> df <- data.frame(var1,var2,var3,fac1,fac2, row.names=NULL, check.rows=TRUE)

# creates this:
  var1 var2 var3 fac1 fac2
1    1    3    4  hot   TX
2    0    2    3 cold   WI
3    3    8    2 cold   UT

# want to see the names of the columns in the dataset:
> names(df)
[1] "var1" "var2" "var3" "fac1" "fac2"

# change the names:
> names(df) <- c("height", "weight", "nose.length", "temp", "state")
> df
  height weight nose.length temp state
1      1      3           4  hot    TX
2      0      2           3 cold    WI
3      3      8           2 cold    UT

# so, now we have a data.frame, the preferred data structure in R.  Let the magic begin:

> plot(df)