[R] predict.lm() question

From: Chip Barnaby <cbarnaby_at_wrightsoft.com>
Date: Mon, 07 Apr 2008 17:57:08 -0400


Dear R-people ...

I'm a new user. I can't get predict.lm() to produce predictions for new independent data. There are some messages in archived help about this problem, but I still don't see my error after reviewing those. I understand that the new independent data must have the same name(s) as used when the model was made.

In the example below, predict.lm produces the predictions for the original (model input) data plus a warning message. What I want is predictions for alternative data (in data frame DX in the example).

Thanks,
Chip Barnaby

> D<-data.frame( X=seq(1:10))
> D$Y<-D$X+rnorm( 10)
> D

     X Y

1   1  0.3811634
2   2  1.8770049
3   3  3.5253376
4   4  3.1851957
5   5  3.8088813
6   6  5.7333074
7   7  7.4896623
8   8  7.9394056
9   9  8.6683570
10 10 10.7480675

> lm<-lm( D$Y~D$X)
> summary( lm)

Call:
lm(formula = D$Y ~ D$X)

Residuals:

      Min 1Q Median 3Q Max -0.98812 -0.36354 -0.09808 0.48154 0.88288

Coefficients:

             Estimate Std. Error t value Pr(>|t|)
(Intercept) -0.58935    0.41680  -1.414    0.195
D$X          1.07727    0.06717  16.037 2.29e-07 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.6101 on 8 degrees of freedom
Multiple R-Squared: 0.9698,     Adjusted R-squared: 0.9661
F-statistic: 257.2 on 1 and 8 DF,  p-value: 2.293e-07


> DX<-data.frame( X=seq( 5.5, 11.5))
> DX
X 1 5.5 2 6.5 3 7.5 4 8.5 5 9.5 6 10.5 7 11.5
> predict.lm( lm, DX)
1 2 3 4 5 6 7 0.4879174 1.5651887 2.6424600 3.7197313 4.7970026 5.8742739 6.9515453 8 9 10 8.0288166 9.1060879 10.1833592 Warning message: 'newdata' had 7 rows but variable(s) found have 10 rows
>
--------------------------------------------------------- Chip Barnaby cbarnaby_at_wrightsoft.com Vice President of Research Wrightsoft Corp. 781-862-8719 x118 voice 131 Hartwell Ave 781-861-2058 fax Lexington, MA 02421 www.wrightsoft.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.
Received on Mon 07 Apr 2008 - 22:06:39 GMT

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