What is graph brushing?

Brushing is selecting one or more data points on a graph to identify the corresponding worksheet information. Use brushing to investigate the characteristics of data points of interest, for example:
  • Identify the worksheet rows that contain the outliers.
  • Determine whether points in a brushing region share other characteristics.

Example of brushing

You create a scatterplot of Yield vs. Input, and notice three points that seem to be outliers. You can brush these points to identify the worksheet rows that contain the data for these points.

Scatterplot with brushed points

Brushed points are a different color.

When you are in brushing mode, the Brushing palette appears. The Brushing palette lists the worksheet row numbers that contain the brushed points, so that you can find them in the worksheet. In the worksheet, the rows that correspond to the brushed points are identified by symbols beside the row numbers.

Brushing palette
Worksheet with brushed rows
In the worksheet in the illustration, the brushed values in the Yield column seem unusually high. To investigate, you can do the following:
  • Look for data-entry errors and correct them.
  • Consider other variables that may explain the high Yield values.
  • Recreate your graph excluding (or including) the brushed points, so that you can examine the data you are most interested in.
  • Subset your worksheet to exclude (or include) brushed points so that you can analyze the corresponding data.

How to brush data points on a graph

With the graph active, choose Editor > Brush. Then, do any of the following:
  • To brush a single point, click it.
  • To brush several adjacent points, drag to enclose the points in a brushing region.
  • To brush individual points that are not adjacent, press and hold the Shift key while clicking the points.
  • To add brushed points to the brushing region, drag the brushing region over them while pressing the Shift key.

To exit brushing mode, choose Editor > Select.

Note

When you brush points in one graph, Minitab automatically brushes points from the same row in all other graphs that are in brushing mode. This is true whether the graphs are in the same Graph window or in other Graph windows. Brushing across graphs can help you investigate relationships across many variables.

Display more information about data points in the Brushing palette

To view more information about the brushed points, you can add variables from the worksheet to the Brushing palette. These variables are called ID variables.

Brushing palette with ID variables

The ID variables in the brushing palette are Yield and Input.

To display ID variables in the palette, first brush the points on the graph. With the graph active, choose Editor > Set ID Variables. In Variables, enter the variables that you want to appear in the Brushing palette.

Add indicator variables to the worksheet based on brushed points

You can create a column in the worksheet to use as an indicator variable that identifies brushed rows with a value of 1 and unbrushed rows with a value of 0 (by default). You can use the indicator variable as a grouping variable for other operations or analyses, such as subsetting worksheets and regression analysis.

To add indicator variables to the worksheet, first brush points on the graph. With the graph active, choose Editor > Create Indicator Variable. In Column, enter a name or column number for the indicator variable column.

Graph a subset of your data based on brushed points

For most graphs on the Graph menu, you can create another graph either by including only brushed points or by excluding all brushed points.

First, brush the points that you want to include or exclude from the new graph. Choose the graph or control chart that you want to create. Click Data Options. On the Subset tab, under Include or Exclude, specify whether you want to include or exclude the brushed rows. Under Specify which rows to include, choose Brushed rows.

Which graphs can be brushed?

The following graphs can be brushed:
  • Scatterplots
  • Matrix plots
  • Bubble plots
  • Marginal plots
  • Dotplots (when each symbol represents only one observation)
  • Probability plots from the Graph menu
  • Empirical CDF plots
  • Individual value plots
  • Time series plots
  • 3D scatterplots
  • Control charts for individuals, except for MR chart
  • Attributes charts
  • T-Squared generalized variance charts (when the subgroup size equals 1)
  • T-Squared charts (when the subgroup size equals 1)
  • Generalized variance charts (when the subgroup size equals 1)
  • Symmetry plots
  • Gage run charts
  • Trend analysis charts
  • Decomposition charts
  • Moving average plots
  • Single exponential smoothing plots
  • Double exponential smoothing plots
  • Winters' method plots
The following graphs cannot be brushed:
  • Histograms
  • Dotplots (when symbols represent more than one observation)
  • Stem-and-leaf plots
  • Boxplots
  • Interval plots
  • Bar charts
  • Pie charts
  • Area graphs
  • Run charts
  • Probability distribution plot
  • Line plot
Note

Brushing is not available for graphs in which points represent more than one worksheet row. For example, if data for all subgroups are in one column and each point on a control chart represents the mean of a subgroup, brushing is not available.

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