row/col-Sums/Means and unit tests - for #549

[nathan-russell]

As discussed in #549, this commit adds Sugar functions for rowSums, colSums, rowMeans, and colMeans, along with unit tests.

[eddelbuettel]

That looks like it is really nice work, once again. Thank so much!

[kevinushey]

Minor style quip, but I think it's a preferable to receive arguments that will be mutated by pointer, rather than by reference -- it makes it more obvious at the call site whether a passed-in parameter might be mutated. For example,

do_something(x);

versus

do_something(&x);

In the first case, I think the expectation most would have is that do_something(x) will not mutate x, whereby it's more obvious that mutation might happen with do_something(&x).

The main downside is the fact that pointers can be NULL while references can't, but I think the clarity in code makes up for that. I'll let others weigh on whether that change is worth making.

[jjallaire]

I agree with Kevin, especially in the case where by local idiom there is no
possibility of the pointer being NULL (which BTW would already be true if
you can pass a reference there).

On Sun, Sep 4, 2016 at 9:38 PM, Kevin Ushey notifications@github.com
wrote:

In inst/include/Rcpp/sugar/functions/rowSums.h
#551 (comment):

+}
+
+inline bool check_na(Rboolean x) {

• return x == NA_LOGICAL;
  +}

+inline bool check_na(SEXP x) {

• return x == NA_STRING;
  +}

+inline bool check_na(Rcomplex x) {

• return ISNAN(x.r) || ISNAN(x.i);
  +}

+inline void incr(double& lhs, double rhs) {

Minor style issue, but I think it's a preferable to receive arguments that
will be mutated by pointer, rather than by reference -- it makes it more
obvious at the call site whether a passed-in parameter might be mutated.
For example,

do_something(x);

versus

do_something(&x);

In the first case, I think the expectation most would have is that
do_something(x) will not mutate x, whereby it's more obvious that
mutation might happen with do_something(&x).

The main downside is the fact that pointers can be NULL while references
can't, but I think the clarity in code makes up for that. I'll let others
weigh on whether that change is worth making.

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[eddelbuettel]

No strong feelings on pointers (clearer as @kevinushey says) versus references (bettern 'modern' C++ ?).

[kevinushey]

Same #undef here?

[kevinushey]

Barring some very minor stylistic suggestions, LGTM!

[eddelbuettel]

Thanks @kevinushey . We'll see if @nathan-russell has time for a revision, else we can probably take it as is.

[nathan-russell]

Those are reasonable suggestions; thanks for reviewing everyone.