Re: [R] Why does plot() ignore the data type for axis labels?

From: Mark Difford <mark_difford_at_yahoo.co.uk>
Date: Wed, 20 Feb 2008 00:26:35 -0800 (PST)

Hi Stiffler,

Duncan Murdoch wrote:

>> The point is that a scatterplot is a graph of real numbers, not of
>> integers.  
>> Use a plot designed for a discrete data type if you don't want things 
>> displayed as their real values ...

To drive home Duncan's point (not that it needs it) ...and to complete the loop, consider how R treats factors:

> x

[1] 1 2 3
> factor(x)

[1] 1 2 3
Levels: 1 2 3

## And:
> factor(x, labels=c("one", "two", "three"))
[1] one two three
Levels: one two three

> unclass(factor(x, labels=c("one", "two", "three")))
[1] 1 2 3
attr(,"levels")
[1] "one" "two" "three"

It does, in the end, make perfect sense.

HTH, Mark.

Duncan Murdoch-2 wrote:
>
> On 19/02/2008 5:40 PM, Stiffler wrote:

>> 
>> 
>> Mark Difford wrote:
>>>>> I was wondering why the plot() command ignores the datatype when
>>>>> displaying axis labels...
>>> plot() doesn't ignore the datatype:
>>> [...]
>>> plot(x,y) calls xy.coords(), which recasts x as: x = as.double(x), which
>>> is fine, since x is (also/primarily) numeric.
>>>
>>> HTH, Mark.
>>>
>>>
>> 
>> Thanks for the explanation Mark.
>> 
>> If integers are being recast as doubles R is ignoring/overriding the
>> user's
>> choice of data-type. There may be good reasons for doing that internally
>> (uniformity, code re-use etc) , but it is not what I'd expect as an
>> end-user
>> --- neither ?plot nor ?xy.coords seem to mention that coordinates need to
>> be
>> floating point numbers.

>
> They don't need to be floating point numbers, they are converted if not.
>
> The point is that a scatterplot is a graph of real numbers, not of
> integers. Use a plot designed for a discrete data type if you don't
> want things displayed as their real values (see for example barplot,
> stripchart, dotchart, etc.)
>
> Duncan Murdoch
>
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