python-dataframe如何计算多条件下的重复次数

data['次数']=1 #新建用来统计出现次数的列，并且初始值为1
for index in range(0,len(data)):
    for index2 in range(index + 1, len(data)):
        if data['销售员'].loc[index] == data['销售员'].loc[index2] and data['物料编码'].loc[index] == data['物料编码'].loc[index2] and data['客户'].loc[index] == data['客户'].loc[index2]:#计算重复的条件设置，引号里面为列名
            data['次数'].loc[index] += 1
            data['次数'].loc[index2] += 1