R help - Nov 2006 - predict.lm "variables found" question

hello,

I'm trying to predict some values based on a linear regression model.
I've created the model using one dataframe, and have the prediction
values in a second data frame (call it newdata). There are 56 rows in
the dataframe used to create the model and 15 in newdata.

I ran predict(model1, newdata) and get the warning: 'newdata' had 15
rows but variable(s) found have 56 rows

When i checked help(predict.lm) I found this:

"Variables are first looked for in newdata and then searched for in
the usual way (which will include the environment of the formula used
in the fit). A warning will be given if the variables found are not of
the same length as those in newdata if it was supplied. "

My questions are - how can I just get predicted values for the 15 rows
in the newdata data frame, and if that's not possible, how can I tell
which of the 56 predicted values are derived from newdata only, if
any.

Thanks in advance for your help.

Larry

"Larry White" <ljw1001 at gmail.com> writes:
> hello,
> 
> I'm trying to predict some values based on a linear regression model.
> I've created the model using one dataframe, and have the prediction
> values in a second data frame (call it newdata). There are 56 rows in
> the dataframe used to create the model and 15 in newdata.
> 
> I ran predict(model1, newdata) and get the warning: 'newdata' had
15
> rows but variable(s) found have 56 rows
> 
> When i checked help(predict.lm) I found this:
> 
> "Variables are first looked for in newdata and then searched for in
> the usual way (which will include the environment of the formula used
> in the fit). A warning will be given if the variables found are not of
> the same length as those in newdata if it was supplied. "
> 
> My questions are - how can I just get predicted values for the 15 rows
> in the newdata data frame, and if that's not possible, how can I tell
> which of the 56 predicted values are derived from newdata only, if
> any.
You need to have all your predictors represented in newdata. You seem
to have at least one of them missing (a typo in a variable name could
do that). 

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