[R] curve() doesn't seem to use the whole range of x? And Error: longer object length is not a multiple of shorter object length

[Matti Viljamaa]

Okay here’s a pretty short code to reproduce it:

data <- read.table("http://users.jyu.fi/~slahola/files/glm1_datoja/yoruotsi.txt", header=TRUE)
attach(data)

fit2 <- lm(ruotsi.pist ~ mies + koulu + lka + koulu*clka)

bs <- coef(fit2)

varitB <- c(data[koulu == 'B',]$mies)
varitB[varitB == 0] = 2
plot(data[data$koulu == 'B',]$lka, data[koulu == 'B',]$ruotsi.pist, col=varitB, pch=16, xlab='', ylab='', main='Lukio B’)

curve(bs["(Intercept)"]+bs["mies"]*0+bs["kouluB"]+bs["lka"]*x+bs["kouluB:clka"]*clka, from=min(lka), to=max(lka), add=TRUE, col='red')


> On 25 Sep 2016, at 19:24, Jeff Newmiller <jdnewmil at dcn.davis.ca.us> wrote:
> 
> Go directly to C. Do not pass go, do not collect $200.
> 
> You think curve does something, but you are missing what it actually does. Since you don't seem to be learning from reading ?curve or from our responses, you need to give us an example you can learn from. 
> -- 
> Sent from my phone. Please excuse my brevity.
> 
> On September 25, 2016 9:04:09 AM PDT, mviljamaa <mviljamaa at kapsi.fi> wrote:
>> On 2016-09-25 18:52, Jeff Newmiller wrote:
>>> You seem to be confused about what curve is doing vs. what you are 
>>> doing.
>> 
>> But my x-range in curve()'s parameters from and to should be the entire
>> 
>> lka vector, since they are from=min(lka) and to=max(lka). Then why does
>> 
>> this not span the entire of lka? Because of duplicate entries or what?
>> 
>> It seems like I cannot use curve(), since my x-axis must be exactly lka
>> 
>> for the function to plot the y value for every lka value.
>> 
>>> A) Compute the points you want to plot and put them into 2 vectors.
>>> Then figure out how to plot those vectors. Then (perhaps) consider
>>> putting that all into one line of code again.
>>> 
>>> B) The predict function is the preferred way to compute points. It
>> may
>>> be educational for you to do the computations by hand at first, but
>> in
>>> the long run using predict will help you avoid problems getting the
>>> equations right in multiple places in your script.
>>> 
>>> C) Learn what makes an example reproducible (e.g. [1] or [2]), and
>> ask
>>> your questions with reproducible code and data so we can give you
>>> concrete responses.
>>> 
>>> [1] http://adv-r.had.co.nz/Reproducibility.html
>>> [2]
>>> 
>> http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example
>>> --
>>> Sent from my phone. Please excuse my brevity.
>>> 
>>> On September 25, 2016 8:36:49 AM PDT, mviljamaa <mviljamaa at kapsi.fi> 
>>> wrote:
>>>> On 2016-09-25 18:30, Duncan Murdoch wrote:
>>>>> On 25/09/2016 9:10 AM, Matti Viljamaa wrote:
>>>>>> Writing:
>>>>>> 
>>>>>> 
>>>> 
>> bs["(Intercept)"]+bs["mies"]*0+bs["kouluB"]+bs["lka"]*lka+bs["kouluB:clka"]*clka
>>>>>> 
>>>>>> i.e. without that being inside curve produces a vector of length
>>>> 375.
>>>>>> 
>>>>>> So now it seems that curve() is really skipping some
>> lka-/x-values.
>>>>> 
>>>>> How could curve() know what the length of lka is?  You're telling
>> it
>>>>> to set x to a sequence of values of length 101 (the default) from
>>>>> min(lka) to max(lka).  You never tell it to set x to lka.
>>>>> 
>>>>> curve() is designed to plot expressions or functions, not vectors.
>>>> If
>>>>> you actually want to plot line segments using your original data,
>> use
>>>>> lines().  (You'll likely need to sort your x values into increasing
>>>>> order if you do that, or you'll get a pretty ugly plot.)
>>>>> 
>>>>> Duncan Murdoch
>>>> 
>>>> I know that about curve(), but since this function uses lka as a
>>>> parameter, then how should I formulate it for curve so that I don't 
>>>> get
>>>> 
>>>> the error about wrong lengths?
>>>> 
>>>>>> 
>>>>>>> On 25 Sep 2016, at 16:01, Matti Viljamaa <mviljamaa at kapsi.fi>
>>>> wrote:
>>>>>>> 
>>>>>>> I’m trying to plot regression lines using curve()
>>>>>>> 
>>>>>>> The way I do it is:
>>>>>>> 
>>>>>>> bs <- coef(fit2)
>>>>>>> 
>>>>>>> and then for example:
>>>>>>> 
>>>>>>> 
>>>> 
>> curve(bs["(Intercept)"]+bs["mies"]*0+bs["kouluB"]+bs["lka"]*x+bs["kouluB:clka"]*clka,
>>>> 
>>>>>>> from=min(lka), to=max(lka), add=TRUE, col='red')
>>>>>>> 
>>>>>>> This above code runs into error:
>>>>>>> 
>>>>>>> Error in curve(bs["(Intercept)"] + bs["mies"] * 0 + bs["kouluB"]
>> +
>>>>>>> bs["lka"] *  :
>>>>>>> 'expr' did not evaluate to an object of length 'n'
>>>>>>> In addition: Warning message:
>>>>>>> In bs["(Intercept)"] + bs["mies"] * 0 + bs["kouluB"] + bs["lka"]
>> *
>>>> :
>>>>>>> longer object length is not a multiple of shorter object length
>>>>>>> 
>>>>>>> Which I’ve investigated might be related to the lengths of the
>>>>>>> different objects being multiplied or summed.
>>>>>>> Taking length(g$x) or length(g$y) of
>>>>>>> 
>>>>>>> g <-
>> curve(bs["(Intercept)"]+bs["mies"]*0+bs["kouluB"]+bs["lka"]*x,
>>>> 
>>>>>>> from=min(lka), to=max(lka), add=TRUE, col='red')
>>>>>>> 
>>>>>>> returns 101.
>>>>>>> 
>>>>>>> However length(lka) is 375. But perhaps these being different is
>>>> not
>>>>>>> the problem?
>>>>>>> 
>>>>>>> I however do see that the whole range of lka is not plotted, for
>>>> some
>>>>>>> reason. So how can I be sure
>>>>>>> that it passes through all x-values in lka? And i.e. that the
>>>> lengths
>>>>>>> of objects inside curve() are correct?
>>>>>>> 
>>>>>>> What can I do?
>>>>>> 
>>>>>> ______________________________________________
>>>>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>>>> PLEASE do read the posting guide
>>>>>> http://www.R-project.org/posting-guide.html
>>>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>>> 
>>>> 
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>