R help - Feb 2013 - Problems plotting and regression w.r.t. date data type on x axis

Hello,

probably a newbie question, but i didnt find any information on
plotting/regressing w.r.t. a date data type. My trials were unfruitful. Can
anyone help ? Thanks in advance!

Here is my interaction with R:

> tabelle
date number date2
1 2009-01-1 1673 2009-01-01
2 2009-12-1 2111 2009-12-01
3 2010-7-1 2487 2010-07-01
4 2013-2-1 4301 2013-02-01
> regression.punkte<-lm(tabelle$number ~ tabelle$date2)
Fehler in model.frame.default(formula = tabelle$number ~ tabelle$date2, :
ung?ltiger Typ (list) f?r die Variable
'tabelle$date2'
> regression.punkte<-lm(tabelle$number ~ tabelle$date)
> plot(tabelle$date2,tabelle$number, pch=19, xlab="date of
retrieval",
> ylab="number of animals") ***R DRAWS THIS***
> regression.punkte
Call:
lm(formula = tabelle$number ~ tabelle$date)

Coefficients:
(Intercept) tabelle$date2009-12-1 tabelle$date2010-7-1
1673 438 814
tabelle$date2013-2-1
2628
> abline(regression.punkte, lwd=2) ***R DOES NOT DRAW LINE***
Warnmeldung:
In abline(regression.punkte, lwd = 2) :
nutze nur die ersten beiden von 4
Regressionskoeffizienten
> summary(regression.punkte)
Call:
lm(formula = tabelle$number ~ tabelle$date)

Residuals:
ALL 4 residuals are 0: no residual degrees of freedom!

Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 1673 NA NA NA
tabelle$date2009-12-1 438 NA NA NA
tabelle$date2010-7-1 814 NA NA NA
tabelle$date2013-2-1 2628 NA NA NA

Residual standard error: NaN on 0 degrees of freedom
Multiple R-squared: 1, Adjusted R-squared: NaN
F-statistic: NaN on 3 and 0 DF, p-value: NA



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Hi

most probably your dates are not what you expect. Eg. they look like a date but
they are not treated as date. You can check yourself by

str(tabelle)

which will result probably in factor, numeric, factor.

You need to change variables date and date2 into Date class.

?strptime or ?as.Date

date and date2 seems to be same but usually you shall use the same variables for
plotting and for model to get correct regression line.

Regards
Petr
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Kategoricus
> Sent: Thursday, February 14, 2013 10:10 AM
> To: r-help at r-project.org
> Subject: [R] Problems plotting and regression w.r.t. date data type on
> x axis
> 
> Hello,
> 
> probably a newbie question, but i didnt find any information on
> plotting/regressing w.r.t. a date data type. My trials were unfruitful.
> Can anyone help ? Thanks in advance!
> 
> Here is my interaction with R:
> 
> 
> > tabelle
> date number date2
> 1 2009-01-1 1673 2009-01-01
> 2 2009-12-1 2111 2009-12-01
> 3 2010-7-1 2487 2010-07-01
> 4 2013-2-1 4301 2013-02-01
> > regression.punkte<-lm(tabelle$number ~ tabelle$date2)
> Fehler in model.frame.default(formula = tabelle$number ~ tabelle$date2,
> :
> ung?ltiger Typ (list) f?r die Variable 'tabelle$date2'
> > regression.punkte<-lm(tabelle$number ~ tabelle$date)
> > plot(tabelle$date2,tabelle$number, pch=19, xlab="date of
retrieval",
> > ylab="number of animals") ***R DRAWS THIS***
regression.punkte
> 
> Call:
> lm(formula = tabelle$number ~ tabelle$date)
> 
> Coefficients:
> (Intercept) tabelle$date2009-12-1 tabelle$date2010-7-1
> 1673 438 814
> tabelle$date2013-2-1
> 2628
> 
> > abline(regression.punkte, lwd=2) ***R DOES NOT DRAW LINE***
> Warnmeldung:
> In abline(regression.punkte, lwd = 2) :
> nutze nur die ersten beiden von 4 Regressionskoeffizienten
> > summary(regression.punkte)
> 
> Call:
> lm(formula = tabelle$number ~ tabelle$date)
> 
> Residuals:
> ALL 4 residuals are 0: no residual degrees of freedom!
> 
> Coefficients:
> Estimate Std. Error t value Pr(>|t|)
> (Intercept) 1673 NA NA NA
> tabelle$date2009-12-1 438 NA NA NA
> tabelle$date2010-7-1 814 NA NA NA
> tabelle$date2013-2-1 2628 NA NA NA
> 
> Residual standard error: NaN on 0 degrees of freedom Multiple R-
> squared: 1, Adjusted R-squared: NaN
> F-statistic: NaN on 3 and 0 DF, p-value: NA
> 
> 
> 
> --
> View this message in context: http://r.789695.n4.nabble.com/Problems-
> plotting-and-regression-w-r-t-date-data-type-on-x-axis-tp4658518.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> 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.

On Feb 14, 2013, at 1:10 AM, Kategoricus wrote:
> Hello,
>
> probably a newbie question, but i didnt find any information on
> plotting/regressing w.r.t. a date data type. My trials were  
> unfruitful. Can
> anyone help ? Thanks in advance!
>
> Here is my interaction with R:
>
>
>> tabelle
> date number date2
> 1 2009-01-1 1673 2009-01-01
> 2 2009-12-1 2111 2009-12-01
> 3 2010-7-1 2487 2010-07-01
> 4 2013-2-1 4301 2013-02-01
>> regression.punkte<-lm(tabelle$number ~ tabelle$date2)
> Fehler in model.frame.default(formula = tabelle$number ~ tabelle 
> $date2, :
> ung?ltiger Typ (list) f?r die Variable 'tabelle$date2'
I'm guessing that you used as.POSIXlt to create that date2 variable.  
POSIXlt classed variables are lists and as such create all sorts of  
problems for functions that are expecting atomic vectors. If I'm  
right, you will ahve better chances of success by converting to  
POSIXct class.

 > tabelle <- read.table(text="date number date2
+ 1 2009-01-1 1673 2009-01-01
+ 2 2009-12-1 2111 2009-12-01
+ 3 2010-7-1 2487 2010-07-01
+ 4 2013-2-1 4301 2013-02-01", header=TRUE, stringsAsFactors=FALSE)
 > tabelle$date2 <- as.POSIXlt(tabelle$date2)
 > regression.punkte<-lm(tabelle$number ~ tabelle$date2)
Error in model.frame.default(formula = tabelle$number ~ tabelle 
$date2,  :
   invalid type (list) for variable 'tabelle$date2'

 > tabelle$date2 <- as.POSIXct(tabelle$date2)
 > regression.punkte<-lm(tabelle$number ~ tabelle$date2)
 > regression.punkte

Call:
lm(formula = tabelle$number ~ tabelle$date2)

Coefficients:
   (Intercept)  tabelle$date2
    -2.405e+04      2.082e-05

>> regression.punkte<-lm(tabelle$number ~ tabelle$date)
>> plot(tabelle$date2,tabelle$number, pch=19, xlab="date of
retrieval",
>> ylab="number of animals") ***R DRAWS THIS***
>> regression.punkte
>
> Call:
> lm(formula = tabelle$number ~ tabelle$date)
>
> Coefficients:
> (Intercept) tabelle$date2009-12-1 tabelle$date2010-7-1
> 1673 438 814
> tabelle$date2013-2-1
> 2628
>
>> abline(regression.punkte, lwd=2) ***R DOES NOT DRAW LINE***
> Warnmeldung:
> In abline(regression.punkte, lwd = 2) :
> nutze nur die ersten beiden von 4 Regressionskoeffizienten
>> summary(regression.punkte)
>
> Call:
> lm(formula = tabelle$number ~ tabelle$date)
>
> Residuals:
> ALL 4 residuals are 0: no residual degrees of freedom!
>
> Coefficients:
> Estimate Std. Error t value Pr(>|t|)
> (Intercept) 1673 NA NA NA
> tabelle$date2009-12-1 438 NA NA NA
> tabelle$date2010-7-1 814 NA NA NA
> tabelle$date2013-2-1 2628 NA NA NA
>
> Residual standard error: NaN on 0 degrees of freedom
> Multiple R-squared: 1, Adjusted R-squared: NaN
> F-statistic: NaN on 3 and 0 DF, p-value: NA
>
>
David Winsemius, MD
Alameda, CA, USA

as.POSIXct() works fine (finally!)

Thanks a lot David&Petr for your help!



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