[R] Predictably puzzled.
bgunter@4567 @end|ng |rom gm@||@com
Sat Nov 20 03:35:23 CET 2021
"predict.lm produces predicted values, obtained by evaluating the
regression function in the frame newdata (which defaults to
1 1.37095845 -0.30663859
2 -0.56469817 -1.78130843
4 0.63286260 1.21467470
6 -0.10612452 -0.43046913
7 1.51152200 -0.25726938
8 -0.09465904 -1.76316309
9 2.01842371 0.46009735
10 -0.06271410 -0.63999488
11 1.30486965 0.45545012
12 2.28664539 0.70483734
13 -1.38886070 1.03510352
16 0.63595040 -1.71700868
17 -0.28425292 -0.78445901
18 -2.65645542 -0.85090759
19 -2.44046693 -2.41420765
20 1.32011335 0.03612261
i.e. only the rows that are used to fit the model are present.
On Fri, Nov 19, 2021 at 6:12 PM Rolf Turner <r.turner using auckland.ac.nz> wrote:
> Consider the following toy example:
> y <- rnorm(20)
> x <- rnorm(20)
> y[c(3,5,14,15)] <- NA
> fit <- lm(y~x)
> This for some reason, which escapes me, does not provide predicted
> values when the response/dependent variable is missing, despite
> there being no missing values in the predictor/independent variable.
> I can get predicted values for all values of x if I set
> ddd <- data.frame(y=y,x=x)
> and execute
> Note that y is (unnecessarily) included in ddd. I thought that
> predict() might omit any rows of the data in which there are missing
> values, but not so.
> OK. I have a workaround which gives me the predicted values that I
> want, but:
> (a) Why does predict() behave in this way? It makes no sense to me,
> but I figure there *must* be a rationale.
> (b) Is there a way of getting predict() to behave as I would like, by
> specifying an appropriate value for na.action? I could not find such
> an appropriate value.
> Thanks for any enlightenment.
> Rolf Turner
> Honorary Research Fellow
> Department of Statistics
> University of Auckland
> Phone: +64-9-373-7599 ext. 88276
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