Specifying Subsets of Data in Excel Using ReadMatrix

Introduction

• Objective: Learn how to specify a subset of data within an Excel worksheet to import using ReadMatrix.
• Reasons for Importing Subsets:
  • Avoid importing non-numeric data as NaN.
  • Only a subset of data may be needed to achieve processing goals.

Specifying Data Subsets

Use of Name-Value Pairs

• Name used: range
• Value: Can take several forms to define a rectangular block of data.

Methods to Specify Rectangular Blocks

1. Opposite Corners:
   • Specify two opposite corners of the block.
   • Can be either of the two pairs and specified in any order (4 combinations).
2. Top Left Corner:
   • Specify the top left corner.
   • ReadMatrix determines the bottom-most row and right-most column with data.

Additional Methods

• Subset of Columns:
  • Specify columns to read.
  • Ignores leading blank rows and headers that are non-numeric.
• Subset of Rows:
  • Specify rows to import.
  • Ignores leading blank columns but imports leading text columns as NaN.

Examples

Example 1: Reading Last Three Columns

• Method 1: Specify top left corner, e.g., C1
  • Result: Imports the last three columns.
• Method 2: Specify opposing corners, e.g., E1:C4
  • Result: Same as above.
• Method 3: Specify columns, e.g., C:E
  • Result: Same as above.

Example 2: Reading Interior Values

• Method: Specify opposing corners, e.g., B2:D3
  • Note: Cannot specify just columns or the upper left corner due to additional row/column inclusion.

Example 3: Avoiding Non-Numeric Headers

• Worksheet: Demo6
• Avoid importing column A as NaN:
  • Method 1: Specify opposite corners, e.g., B3:F6
  • Method 2: Specify only upper left corner, e.g., B3
  • Method 3: Specify columns, e.g., B:F

Conclusion

• ReadMatrix Behavior: Will not ignore non-numeric columns to the left.
• Future Videos: Continue investigation into subset data reading from Excel.

Notes

• Ensure proper specification of worksheet and range for accurate data import.
• MATLAB documentation is a useful resource for additional options not covered here.