create internal func and put in relevant funcs

[hfuchs5]

What changes are proposed in this pull request?
Changed non-numeric column identification to make sure it stopped printing all of the column names

If there is an GitHub issue associated with this pull request, please provide link.
#314

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[karissawhiting]

This looks good and close to merge!

I think we can simply the .check_numeric() function a bit. We can either stick to base R matrix subsetting (is_numeric <- apply(alt_only, 2, is.numeric), then names(is_numeric[!is_numeric])), or if we want tidyverse I think imap() would be a good option. This maps over input columns and names simultaneously. Then I don't think we would need to create the interstitial dataframe in between input and outputting vector of names for messaging, which I think could slow things down on a large data set.