# Re: [R] problem with lm and predict - no predictions made

From: Erik Iverson <iverson_at_biostat.wisc.edu>
Date: Wed, 02 Jul 2008 20:55:54 -0500

Hello -

Keld Jørn Simonsen wrote:
> Hi
>
> I have a problem with lm and predict
>
> I have
>
> us
> [1] 2789.53 3128.43 3255.03 3536.68 3933.18 4220.25 4462.83 4739.48
> [9] 5103.75 5484.35 5803.08 5995.93 6337.75 6657.40 7072.23 7397.65
> [17] 7816.83 8304.33 8746.98 9268.43 9816.98 10127.95 10469.60 10960.75
> [25] 11685.93 12433.93 13194.70 13843.83
>
>
> us.p
> [1] 227.62 229.92 232.13 234.25 236.31 238.42 240.59 242.75 244.97 247.29
> [11] 250.05 253.39 256.78 260.15 263.33 266.46 269.58 272.82 276.02 279.20
> [21] 282.31 285.25 288.10 290.85 293.53 296.26 299.08 301.97
>
> us.l = lm(log(us) ~ log(us.p))

```>> predict(us.l,n.ahead=5)

>        1        2        3        4        5        6        7        8

> 8.079754 8.131908 8.181531 8.228692 8.274111 8.320224 8.367224 8.413588
>        9       10       11       12       13       14       15       16
> 8.460813 8.509709 8.567285 8.636117 8.705057 8.772694 8.835719 8.897015
>       17       18       19       20       21       22       23       24
> 8.957402 9.019376 9.079867 9.139289 9.196752 9.250495 9.302067 9.351347
>       25       26       27       28
```
> 9.398927 9.446950 9.496094 9.545979
>
>
> Why does predict not give me any predictions? The result of predict() is
> same lenght (28) as the us and us.p variables.

The version of 'predict' being called on 'us.l' (i.e., predict.lm) is doing predictions, and it should be giving you a result of identical length as your original vectors. What are you expecting here? Your usage of the 'n.ahead' parameter suggests to me you might be wanting to fit your model using a different function than 'lm', and use its corresponding prediction function.

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 Thu 03 Jul 2008 - 01:56:50 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Thu 03 Jul 2008 - 08:31:01 GMT.

Mailing list information is available at https://stat.ethz.ch/mailman/listinfo/r-help. Please read the posting guide before posting to the list.