Cleaning up for loops with make_(counting_)transform_iterator

[codereport]

Doing some cleanup - using make_counting_transform_iterator and make_transform_iterator to clean up for loops and other code.

Making an argument that make_counting_transform_iterator should be moved out of cudf::test::.

Also, will clean up the f/begin and op naming conventions.

Depends on: #7306

[GPUtester]

Please update the changelog in order to start CI tests.

View the gpuCI docs here.

[jrhemstad]

Some of these updates could be even cleaner by just using the child iterators.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (branch-0.19@8215b5b). Click here to learn what that means.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             branch-0.19    #6546   +/-   ##
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  Coverage               ?   82.20%           
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  Files                  ?      100           
  Lines                  ?    16966           
  Branches               ?        0           
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  Hits                   ?    13947           
  Misses                 ?     3019           
  Partials               ?        0           

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[harrism]

Nice improvements, and even cleaner with Jake's observation about child iterators.

Please move make_counting_transform_iterator into a libcudf header so we don't have to depend on libcudf_test and so it's available to users of libcudf that are not users of libcudf_test.

[codereport]

Do the following:

// cpp/src/structs/structs_column_view.cu
  std::vector<column_view> children;
  children.reserve(child(index).num_children());
  for (size_type i = 0; i < child(index).num_children(); i++) {
    children.push_back(child(index).child(i));
  }

[harrism]

@codereport should this slip to 0.18?

[jrhemstad]

@codereport do you still plan to complete this? Moving to 0.19.

[davidwendt]

LGTM. Some of the files need a copyright year update.

[codereport]

@gpucibot merge