COUNTA function is similar to COUNTIF function, but it only counts the non-empty cells. 

Description from Microsoft here: https://support.office.com/en-us/article/COUNTA-function-7dc98875-d5c1-46f1-9a82-53f3219e2509?ui=en-US&rs=en-US&ad=US&fromAR=1 .

Workaround: it should be possible to implement such custom function. See Custom Functions help article here: http://docs.telerik.com/devtools/document-processing/libraries/radspreadprocessing/features/formulas/custom-functions .