Dataset.count() every time is different.

Dataset<Row> dataset = sparkSession.read().format("csv").option("sep", ",").option("inferSchema", "true")
.option("escape", Constants.DEFAULT_CSV_ESCAPE).option("header", "true")
.option("encoding", "UTF-8")
.load("hdfs://192.168.1.26:9000/data/caopan/07-08_WithHead30M.csv");

System.out.println("source count="+dataset.count());

Dataset<Row> dropDuplicates = dataset.dropDuplicates(new String[]{"DATE","TIME","VEL","COMPANY"});
System.out.println("dropDuplicates count1="+dropDuplicates.count());
System.out.println("dropDuplicates count2="+dropDuplicates.count());

Dataset<Row> filter = dropDuplicates.filter("jd > 120.85 and wd > 30.666666 and (status = 0 or status = 1)");

System.out.println("filter count1="+filter.count());
System.out.println("filter count2="+filter.count());
System.out.println("filter count3="+filter.count());
System.out.println("filter count4="+filter.count());
System.out.println("filter count5="+filter.count());

------------------------------------------------------The above is code ---------------------------------------

 
 
console output:

source count=459275
dropDuplicates count1=453987
dropDuplicates count2=453987
filter count1=445798
filter count2=445797
filter count3=445797
filter count4=445798
filter count5=445799

question:
 
Why is filter.count() different everytime?

if I remove dropDuplicates() everything will be ok!!