Importing S3 method from another package

Question

I'm trying to import a S3 method, `predict` from another package `pls`. I have a function which uses these predicted values. The problem is, when compiling the package: ``` Error : object 'predict' is not exported by 'namespace:pls' ``` I've put together this Gist as a minimal example which highlights my problem and contains the following R file: ``` #' Test function #' #' @importFrom pls predict #' #' @export myfunc <- function(x){ stopifnot(class(x) == "mvr") predict(x)*2 } ```

Accepted Answer

To summarise this as the original (below) is now out-dated and in places erroneous or misleading.

The proximal issue is that there is no function named `predict` in the pls package; there are some unexported S3 methods for `predict` but no such `predict`. So you can't import this. The `predict` generic lives in the stats package and you'll need to import from there as discussed below.

Your package needs to have `Depends: pls` in the `DESCRIPTION` in order for the correct `predict` method to be available to R. There's nothing in pls that you can specifically import.

You also need to import the `predict` generic from the stats namespace, so add

```
#' @importFrom stats predict
```

as that will import the generic in you packages namespace. You will also want to add `Imports: stats` to your `DESCRIPTION` file to indicate that you need the stats package; previously we didn't have to declare dependencies on the set of base packages shipped with R (i.e. the non-Recommended ones that ship with R).

Original

The main issue here is the pls doesn't define a function/method `predict`. It provides several methods for the `predict` generic, but not the generic itself.

You need to import the generic from the stats package, if you need it - I'm not sure you do as you aren't creating a function that needs or builds on the generic. At the minimum you'll need

```
#' @importFrom stats predict
```

though you may need/want to import the entire stats namespace - depends what your package does beyond the function your are currently working on.

The other issue is that `predict.mvr` is not exported from the pls namespace

```
> require(pls)
Loading required package: pls

Attaching package: ‘pls’

The following object(s) are masked from ‘package:stats’:

loadings

> predict.mvr
Error: object 'predict.mvr' not found
> pls::predict.mvr
Error: 'predict.mvr' is not an exported object from 'namespace:pls'
> pls:::predict.mvr
function (object, newdata, ncomp = 1:object$ncomp, comps, type = c("response", 
    "scores"), na.action = na.pass, ...) 
```

As such you can't just import it. Hence your package needs to have `Depends: pls` in the `DESCRIPTION` in order for the correct `predict` method to be found.

Importing S3 method from another package

Solution

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