使用python为组中的每个元素添加序列号 [英] Add a sequence number to each element in a group using python

问题描述

我有一个数据框，每个人都有多个记录.我想在python中为每个人枚举序列中的记录.基本上我想在下表中创建序列"列:

I have a dataframe of individuals who each have multiple records. I want to enumerate the record in the sequence for each individual in python. Essentially I would like to create the 'sequence' column in the following table:

patient  date      sequence
145      20Jun2009        1
145      24Jun2009        2
145      15Jul2009        3
582      09Feb2008        1
582      21Feb2008        2
987      14Mar2010        1
987      02May2010        2
987      12May2010        3

这与 here，但我在 python 中工作并且无法实现 sql 解决方案.我怀疑我可以使用带有可迭代计数的 groupby 语句，但到目前为止还没有成功.谢谢！

This is essentially the same question as here, but I am working in python and unable to implement the sql solution. I suspect I can use a groupby statement with an iterable count, but have so far been unsuccessful. Thanks!

推荐答案

问题是如何对多列数据进行排序.

The question is how do I sort on multiple columns of data.

一个简单的技巧是使用 key 参数到 排序 函数.

One simple trick is to use the key parameter to the sorted function.

您将按由数组的列构建的字符串进行排序.

You'll be sorting by a string built from the columns of the array.

rows = ...# your source data

def date_to_sortable_string(date):
  # use datetime package to convert string to sortable date.
  pass

# Assume x[0] === patient_id and x[1] === encounter date

# Sort by patient_id and date
rows_sorted = sorted(rows, key=lambda x: "%0.5d-%s" % (x[0], date_to_sortable_string(x[1])))

for row in rows_sorted:
  print row

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