You can modify a chart’s data references in the chart data editor. You can enter only numbers, dates, or durations in data cells.
Select the chart, click Edit Chart Data, then do any of the following:
Add a data series: Click a cell in a new column or row, then enter your data.
Delete a data series: Click the colored bar for the row or column you want to delete, click the arrow that appears, then click Delete Column or Delete Row (depending on whether you plotted rows or columns as data series).
Reorder data series: Drag the colored bars to reorder the chart data series.
Close the Chart Data window to return to the chart.
When you add a chart, Keynote defines default data series for it. In most cases, if a table is square or if it’s wider than it is tall, the table rows are the default series. Otherwise, the columns are the default series. You can change whether rows or columns are the data series.
Select the chart, then click Edit Chart Data.
Click a row or column button in the top-right corner of the Chart Data editor.
Close the Chart Data editor when you’re done.
Sharing the x-axis means plotting a single kind of value along the x-axis, while allowing for multiple kinds of values plotted along the y-axis.
Select the chart, then click Edit Chart Data.
Click 
, then select Share X Values.
Close the Chart Data editor when you’re done.