What is Mapper in MapReduce?

Mapper is one of the functions in the MapReduce that is used to process the input data. It processes the data by creating several small chunks of it. The mapper function takes the input in the form of a key/value pairs and processes the data into several chunks. The input data is specified to the Mapper function by the InooutFormat that defines the location of the input data. The RecordReader objects present in the InputFormat are used to extract the key/value from the input source. Then, the Mapper processes the input and creates an intermediate output that is sent o the Reducer.