How to preserve leading zeros with ExcelWriter

Problem

Importing numbers with leadings zeros, such as zip codes and social security numbers, can pose a challenge. While these numbers are most often stored in a database as strings, they can be imported into Excel as either numbers or strings. Importing as numbers is the preferred option, as importing as strings will cause Excel to display a warning message that a number is being displayed as text.

Solution

When importing numbers with leading zeros, you have two options:

  1. Import or insert the values as numbers and not as strings. Set the appropriate special format as needed to display the desired number of leading zeros. This is the recommended practice.
  2. Import or insert the values as strings. Format the cells as General or Text. Excel will display a warning on each cell that a number is displayed as text. However, the cell values will contain the leading zeros.

Option 1: Import numbers with leading zeros as numbers (Recommended)

As mentioned above, the preferred option for importing numbers with leading zeros as numbers. Leading zeros will be stripped off, as numeric data types cannot contain leading zeros. To display the desired number of leading zeros within Excel on these numeric values, the appropriate formatting string should be set on the cells which contain the data.

It should be noted that a limitation to this approach is that when a value is read out of a cell there will be no leading zeros. If you would prefer to have leading zeros stored in the cell values (and have Excel display the warning message instead), you should use Option 2 as described below.

ExcelTemplate

When using ExcelTemplate, you have three options for converting your data from strings to an appropriate numeric data type. You can:

  • Let ExcelTemplate attempt to globally convert all strings to numeric values where appropriate. (This is the default behavior.)
  • Convert the applicable zip code values (and any other numbers) to numeric data types through native features of the language. Then set the PreserveStrings property to true to force ExcelTemplate to preserve all strings as strings. This approach will result in the most predictable results, since setting PreserveStrings to true will prevent ExcelWriter from performing string to numeric data type conversions.
  • Use a combination of Preserve and/or Convert data marker modifiers on specific columns. Which modifiers you use should depends on how PreserveStrings is set. If you choose this option, the recommended practice is to set PreserveStrings to true and use Convert data marker modifiers on zip code columns. For more info about data marker modifiers, please refer to the Creating Data Markers documentation.

Then set the appropriate cell formats on the template for the columns which will contain these values. Use the Zip Code or Social Security formats (listed under the Special category), or use your own custom string.

ExcelApplication

With ExcelApplication, no automatic string to number conversion exists. Therefore, you must convert the applicable zip code data using native features of the language. Set the appropriate cell formats on the existing file, if there is one, or use the ExcelApplication API to set it on an AreaRange, or individual Cell.

When setting the formatting through the ExcelApplication API, you should use the Style.NumberFormat property. For example, to set a zip code format on a cell, you would do:

 myCell.Style.NumberFormat = NumberFormat.Special_EN_US.ZipCode; 

In the above example, the NumberFormat.SpecialENUS.ZipCode constant is equivalent to “00000”. This forces Excel to always display five digits, prepending zeros to the number as necessary.

Option 2: Import numbers with leading zeros as strings

As mentioned above, you can import numbers with leading zeros as strings instead of converting them to numbers. However, Excel will display a warning that a number is displayed as text. This will allow you store the leading zeros in the cell values, preventing the need to set a special cell format, and also allowing the value to be read from the cell so that it includes the leading zero.

ExcelTemplate

To preserve strings using ExcelTemplate, use a combination of the following techniques:

  • Set the global PreserveStrings property to true.
  • Use a combination of Preserve and/or Convert data marker modifiers on specific columns. Which modifiers you use depends on how PreserveStrings is set.

Set the applicable cell formats to General or Text in the template.

For more information about using ExcelTemplate to convert strings to numbers where appropriate, please see this post: How to preserve strings with ExcelTemplate.

ExcelApplication

To preserve string values with ExcelApplication, no action is needed. ExcelApplication will always preserve strings, because it provides no automatic conversion functionality.

Set the appropriate cell formats to General or Text, either on the template or using the ExcelApplication API. The following example sets a cell format to Text:

 myCell.Style.NumberFormat = "@";

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