Below is a step‐by‐step guide on how to use wgrib2 to filter out the problematic messages from your GRIB file so that cfgrib no longer sees conflicting keys:
- Linux/Mac: You can often install via your package manager. For example, on Ubuntu:
sudo apt-get install wgrib2
- Windows: Download a precompiled binary from the official site or repository.
First, generate a summary of the GRIB messages. This lets you inspect metadata such as parameter names, step values, and step types. Run:
wgrib2 input.grib -s > messages.txt
This command writes a summary to messages.txt. Open this file in a text editor and look for the entries related to your problematic variable (e.g., lines containing swvl2). Note the associated stepType (or similar keywords) and other details.
From the summary:
- Look at the messages for
swvl2 and check for the step values and stepType (or similar tags).
- Decide which step type (for example,
avgid, avgd, etc.) represents the correct data you want to work with. This decision might be based on available documentation from your data provider or by comparing multiple records.
Once you’ve identified the appropriate stepType (say it is avgid), you can filter the file so that only records with that step type remain. Run:
wgrib2 input.grib -match ":stepType:avgid:" -grib_out filtered.grib
- Explanation:
-match ":stepType:avgid:" selects only the messages that include the text stepType:avgid.
-grib_out filtered.grib writes the selected messages to a new GRIB file called filtered.grib.
Tip: If your summary uses a slightly different keyword format (for example, the tag might not be exactly stepType), adjust the match string accordingly.
To ensure that only the desired messages are included, list the contents of the filtered file:
Review the output to confirm that only messages with the selected step type (and thus consistent step values) remain.
Now that you have a filtered file without conflicting keys, update your Python code to read filtered.grib instead of the original file. This should prevent the error in cfgrib.
- List messages: Generate a summary to inspect the metadata.
- Decide on filter: Determine which step type (e.g.,
avgid) is the correct one.
- Filter file: Use wgrib2’s
-match option to extract only the desired messages.
- Verify: Check the filtered file’s contents.
- Read filtered file: Use the new GRIB file in your Python workflow.
Following these steps should help you avoid the duplicate key error by ensuring only consistent records are passed to cfgrib.