func CountTry(ix *etable.IdxView, colNm string) ([]float64, error) {
	colIdx, err := ix.Table.ColIdxTry(colNm)
	if err != nil {
		return nil, err
	}
	return CountIdx(ix, colIdx), nil
}
CountTry returns the count of non-Null, non-NaN elements in given
IdxView indexed view of an etable.Table, for given column name.
If name not found, returns error message.
Return value is size of each column cell -- 1 for scalar 1D columns
and N for higher-dimensional columns.
package agg
import (
	"math"
	"github.com/emer/etable/etable"
)
type IdxViewAggFuncIdx func(ix *etable.IdxView, colIdx int) []float64
type IdxViewAggFunc func(ix *etable.IdxView, colIdx int) []float64
type IdxViewAggFuncTry func(ix *etable.IdxView, colIdx int) ([]float64, error)
func CountIdx(ix *etable.IdxView, colIdx int) []float64 {
	return ix.AggCol(colIdx, 0, CountFunc)
}
func Count(ix *etable.IdxView, colNm string) []float64 {
	colIdx := ix.Table.ColIdx(colNm)
	if colIdx == -1 {
		return nil
	}
	return CountIdx(ix, colIdx)
}