CODEWITHSUNDEEP
rvector
Eric Baldwin
Eric Baldwin

Reputation: 3491

Are integer vectors numeric vectors in R?

I have an integer vector that I expected I could treat as a numeric vector:

> class(pf$age)
[1] "integer"
> is.numeric(pf$age)
[1] TRUE

However, when I try to use it to calculate a correlation, I get an error:

> cor.test(x = "age", y = "friend_count", data = pf)
Error in cor.test.default(x = "age", y = "friend_count", data = pf) : 
  'x' must be a numeric vector

None of my best guesses at alternate syntax work either: http://pastie.org/9595290

What's going on?

Edit:

The following syntax works:

> x = pf$age
> y = pf$friend_count
> cor.test(x, y, data = pf, method="pearson", alternative="greater")

However, I don't understand why I can't specify x and y in the function (as you can with other R functions like ggplot). What is the difference between ggplot and cor.test?

Upvotes: 1

Views: 1476

Answers (2)

rnso
rnso

Reputation: 24535

You can use 'get' with strings to get data: 

age = pf$age
friend_count = pf$friend_count

or:

attach(pf)

then following should work: 

cor.test(x = get("age"), y = get("friend_count"))

Upvotes: 0

Gavin Simpson
Gavin Simpson

Reputation: 174813

You don't refer to variables using character strings like that in a function call. You want to pass to the x and y arguments numeric vectors. You passed length 1 character vectors:

> is.numeric("age")
[1] FALSE
> is.character("age")
[1] TRUE

Hence you were asking cor.test() to compute the correlation between the strings "age" and "friend_count".

You also mixed up the formula method of cor.test() with the default one. You supply a formula and a data object or you supply arguments x and y. You can't mix and match.

Two solutions are:

  1. with(pdf, cor.test(x = age, y = friend_count))
  2. cor.test( ~ age + friend_count, data = pf)

The first uses the default method, but we allow ourselves to refer to the variables in pf directly by using with(). The second uses the formula method.

As to your question in the title; yes, integer vectors are considered numeric in R:

> int <- c(1L, 2L)
> is.integer(int)
[1] TRUE
> is.numeric(int)
[1] TRUE

Do note @Joshua Ulrich's point in the comment below. Technically integers are slightly different to numerics in R as Joshua shows. However this difference need not concern users most of the time as R can convert/use these as needed. It does matter in some places, such as .C() calls for example.

Upvotes: 2

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