Add rangeBounds parameter to preProcess()

[sergeykorop]

This PR proposes following improvement: by adding new parameter, rangeBounds to preProcess() we will be able to specify an explicit interval for range transformation, e.g. [-0.5, 0.5] instead of [0, 1] used by default.

[codecov-io]

Codecov Report

Merging #730 into master will increase coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #730      +/-   ##
==========================================
+ Coverage   16.97%   17.16%   +0.19%     
==========================================
  Files          90       90              
  Lines       13185    13196      +11     
==========================================
+ Hits         2238     2265      +27     
+ Misses      10947    10931      -16

Impacted Files	Coverage Δ
R/preProcess.R	38.34% <0%> (+3.19%)	⬆️

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[sergeykorop]

This PR interferes with issue #729: unit tests for range transformation of preProcess() are in preProcess_methods.R which is not active for now.

To work-around this issue, I reproduced existing tests related to range in new test file, test_preProcess_range.R and added some new ones covering new functionality. If issue #729 will be settled with bringing preProcess_methods.R back to a pool of active tests, these new tests can be re-integrated back to that file.

[topepo]

Thanks for adding this. You could also get this effect by using the recipes interface to train (just as an fyi)

[topepo]

@sergeykorop Based on the reverse dependency checks, can you make some quick changes to ensure that the new version of range scaling works with objects from previous versions where those objects don't exist?

For example, the printing is off:

> standardObj
Created from 214 samples and 2343 variables

Pre-processing:
  - ignored (0)
  - re-scaling to [, ] (2343)

Also, for old objects, these lines fail:

newdata[, object$method$range] <- sweep(newdata[, object$method$range, 
    drop = FALSE], 2, (object$ranges[2, ] - object$ranges[1, 
    ])/(object$rangeBounds[2] - object$rangeBounds[1]), "/")
newdata[, object$method$range] <- sweep(newdata[, object$method$range, 
    drop = FALSE], 2, object$rangeBounds[1], "+")

[sergeykorop]

@topepo See PR #790 for bug fix.