Hadoop MapReduce Error: Illegal Partition in MapTask - java.io.IOException: Illegal partition for 1660,1998-01-10 (-16)

This error message indicates that there is an illegal partition for a specific key-value pair in the input data. The partition is calculated based on the hash code of the key, and in this case, it seems that the hash code resulted in a negative value (-16), which is not a valid partition number.

To resolve this issue, you can try adjusting the number of reducers or changing the partitioning logic to ensure that all keys are hashed to a valid partition. Additionally, you may want to check the input data to make sure there are no missing or invalid values that could be causing this error.