[R] Problems plotting and regression w.r.t. date data type on x axis

[PIKAL Petr]

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,
> :
> ungültiger Typ (list) für 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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> 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.
> 
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