You can modify a chart’s data references (numbers, dates, or durations) at any time. You can add and remove an entire data series, or edit a data series by adding or deleting specific data from it.
Click 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 in the Chart Data editor, enter your data, then press Return or Tab. Repeat these steps until you’ve entered the entire data series.
Remove a data series: Click the bar for the row or column you want to delete, click the arrow that appears, then click Delete Row or Delete Column (depending on whether you plotted rows or columns as data series).
Reorder data series: Drag a bar to reorder the data series.
Add a currency symbol or other formatting: Click the Series tab at the top of the sidebar on the right, then use the controls to add value labels or other formatting.
Close the Chart Data window to return to the chart.
When you add a chart, Keynote defines the 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.
Click the chart, then click the Edit Chart Data button.
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. By default, the x-axis values are shared among multiple sets of y-axis values in some types of charts.
Click the chart to select it, then click the Edit Chart Data button.
Click 
, then select Share X Values.
Close the Chart Data editor when you’re done.
If a column, bar, line, or area chart references a table with a large number of data points, the chart automatically shows a representative sample of each series to improve the performance of Keynote. Downsampling doesn’t change or remove the data in your table, and only changes the visible data points in the chart.
If your chart data is being downsampled, a message appears when you click Large Data Set in the Chart tab of the Format 
sidebar.
If you want to see certain data points in your chart, you need to create the chart from a smaller table or a smaller selection of data from a large table.