[ML] Improve legend text when chart not available or no data available.

Author: walterra

x-pack/plugins/ml/public/application/components/data_grid/column_chart.tsx

@@ -34,6 +34,7 @@ export const ColumnChart: FC<Props> = ({ chartData, columnType }) => {
           <Chart>
             <Settings
               theme={{
+                background: { color: 'transparent' },
                 chartMargins: {
                   left: 4,
                   right: 4,
@@ -64,7 +65,7 @@ export const ColumnChart: FC<Props> = ({ chartData, columnType }) => {
       )}
       <div
         className={classNames('mlDataGridChart__legend', {
-          'mlDataGridChart__legend--numeric': isNumericChartData(chartData),
+          'mlDataGridChart__legend--numeric': columnType.schema === 'number',
         })}
       >
         {legendText}

x-pack/plugins/ml/public/application/components/data_grid/data_grid.tsx

@@ -180,7 +180,7 @@ export const DataGrid: FC<Props> = memo(
           <EuiDataGrid
             aria-label={isWithHeader(props) ? props.title : ''}
             columns={columnsWithCharts.map((c) => {
-              c.initialWidth = 150;
+              c.initialWidth = 165;
               return c;
             })}
             columnVisibility={{ visibleColumns, setVisibleColumns }}

x-pack/plugins/ml/public/application/components/data_grid/use_column_chart.tsx

@@ -321,9 +321,16 @@ type LegendText = string | JSX.Element;
 const getLegendText = (chartData: ChartData): LegendText => {
   if (chartData.type === 'unsupported') {
     return i18n.translate('xpack.ml.dataGridChart.histogramNotAvailable', {
-      defaultMessage: `Histogram chart not supported for this type of column.`,
+      defaultMessage: 'Chart not supported.',
     });
   }
+
+  if (chartData.data.length === 0) {
+    return i18n.translate('xpack.ml.dataGridChart.notEnoughData', {
+      defaultMessage: `0 documents contain field.`,
+    });
+  }
+
   if (chartData.type === 'boolean') {
     return (
       <table className="mlDataGridChart__legendBoolean">