如何统计json数据中某个字段的唯一值出现的次数？

示例数据：[{"departmentCode": "42902134", "departmentName": "林区统计局"},{"departmentCode": "42902184", "departmentName": "神农架林区城管局"},{"departmentCode": "42902104", "departmentName": "林区发改委"},{"departmentCode": "42902105", "departmentName": "林区教育局"},{"departmentCode": "42902106", "departmentName": "林区科技局"},{"departmentCode": "42902107", "departmentName": "林区经信局"},{"departmentCode": "42902109", "departmentName": "林区公安局"},{"departmentCode": "42902111", "departmentName": "林区民政局"},{"departmentCode": "42902112", "departmentName": "林区司法局"},{"departmentCode": "42902113", "departmentName": "林区财政局"},{"departmentCode": "42902114", "departmentName": "林区人社局"},{"departmentCode": "42902115", "departmentName": "林区自然资源和规划局"},{"departmentCode": "42902116", "departmentName": "林区生态环境局"},{"departmentCode": "42902117", "departmentName": "林区住建局"},{"departmentCode": "42902118", "departmentName": "林区交通运输局"},{"departmentCode": "42902119", "departmentName": "林区水利和湖泊局"},{"departmentCode": "42902120", "departmentName": "林区农业农村局"},{"departmentCode": "42902121", "departmentName": "林区商务局"},{"departmentCode": "42902122", "departmentName": "林区文旅局"},{"departmentCode": "42902123", "departmentName": "林区卫健委"},{"departmentCode": "42902125", "departmentName": "林区应急局"},{"departmentCode": "42902131", "departmentName": "林区市场监督管理局"},{"departmentCode": "42902136", "departmentName": "林区医疗保障局"},{"departmentCode": "42902139", "departmentName": "林区宣传部"},{"departmentCode": "42902141", "departmentName": "林区民宗委"},{"departmentCode": "42902154", "departmentName": "林区气象局"},{"departmentCode": "42902156", "departmentName": "消防大队"},{"departmentCode": "42902164", "departmentName": "林区林业管理局"},{"departmentCode": "42902175", "departmentName": "林区档案局"},{"departmentCode": "42902177", "departmentName": "林区保密局"},{"departmentCode": "42902197", "departmentName": "林区公共资源监管局"},{"departmentCode": "42902198", "departmentName": "林区金融办"},{"departmentCode": "42902134", "departmentName": "林区统计局"},{"departmentCode": "42902184", "departmentName": "神农架林区城管局"},{"departmentCode": "42902104", "departmentName": "林区发改委"},{"departmentCode": "42902105", "departmentName": "林区教育局"},{"departmentCode": "42902106", "departmentName": "林区科技局"},{"departmentCode": "42902107", "departmentName": "林区经信局"},{"departmentCode": "42902109", "departmentName": "林区公安局"},{"departmentCode": "42902111", "departmentName": "林区民政局"}]。

求：输出departmentName字段的唯一值出现的次数，例如：林区统计局：2，神农架林区城管局：2，林区民政局：1...