[R] help with predict.lda

[David Winsemius]

On Jul 4, 2010, at 7:37 AM, David Winsemius wrote:

>
> On Jul 3, 2010, at 11:33 PM, Changbin Du wrote:
>
>> HI, Dear community,
>>
>> I am using the linear discriminant analysis to build model and make  
>> new
>> predictions:
>>
>>> dim(train)  #training data
>> [1] 1272   22
>>> dim(valid)  # validation data
>> [1] 140  22
>>
>>
>> lda.fit <- lda(out ~ ., data=train, na.action="na.omit", CV=TRUE) #  
>> model
>> fitting of linear discriminant analysis on training data
>>
>>> predict(lda.fit, valid)   # make prediction on validation data
>> Error in UseMethod("predict") :
>> no applicable method for 'predict' applied to an object of class  
>> "list"
>
> The predict methods are very picky with what can be used as input.  
> They need to have a dataframe with exactly the same variable names  
> as were used in the rhs of the formula given to the fitting function.

That is still mostly true except that it should say "includes all of  
the variables used in the rhs".

> In this case that would be all columns in "train" except $out.  
> Reasoning under the assumption that "valid" looks just like "train"  
> at the moment, I think it's possible that you need to remove the  
> "$out" column from the "valid" object since it was not on the rhs.

That is not correct. The example in MASS::lda clearly shows the use of  
a dataframe that has the grouping variable left in a dataframe offered  
to predict().

> Of course it is also possible that "valid" is even more poorly  
> constructed than I think, so any further questions should adhere to  
> Peter's admonitions as well as including str(train) and str(valid).

So that is even "more true".

>
>
>>
>> Can anyone help with this?
>>
> -- 
>
> David Winsemius, MD
> West Hartford, CT
>
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David Winsemius, MD
West Hartford, CT