charnum( c(
'123', '$50.02', '30%', '(300.01)', '-10', '1 230.4', NA, '-', '', "3.7999999999999999E-2"
))
charnum( c( '123', 'abc', '30%', NA) )
# returns FALSE since this can be converted to a date:
charnum( c( '20180101' ))
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