Left join and ValueError: Wrong number of items passed 55, placement implies 1

Question

我有两个数据框

一大：myTradeFrame (7401x27)
一小块：specialsData (3x3)

specialsData 看起来像这样：

   coll_cusip tran_type  maturity_max
0  912810SC3        BB          1.80
1  912810SD1        BB          1.76
2  9128284V9        BB          1.08

然后代码是这样的：

myTradeFrame['NewColumn']=pd.merge(myTradeFrame, specialsData, how='left', left_on = ['coll_cusip','tran_type'], right_on=[ 'coll_cusip', 'tran_type'])

这行代码给我一个错误，即使键列存在于两个数据帧中。我错过了什么？

the error message i get is : 
    len(self.mgr_locs)))
ValueError: Wrong number of items passed 55, placement implies 1
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/apps/qtrinst/install/python/anaconda/envs/sx_anaconda/lib/python3.5/site-packages/IPython/core/interactiveshell.py", line 2850, in run_ast_nodes
    if self.run_code(code, result):
  File "/apps/qtrinst/install/python/anaconda/envs/sx_anaconda/lib/python3.5/site-packages/IPython/core/interactiveshell.py", line 2927, in run_code
    self.showtraceback(running_compiled_code=True)
TypeError: showtraceback() got an unexpected keyword argument 'running_compiled_code'

基本上，myTradeFrame 中的 NewColumn 应该在交集 coll_cusip 和 tran_type

处具有列 "maturity_max" 的值

Answer 1

pd.merge returns 分配给单个列的数据框。因此错误。您可以将您的代码代码替换为以下

myTradeFrame = pd.merge(myTradeFrame, specialsData, how='left', on=[ 'coll_cusip', 'tran_type'],suffixes=('_left','_right'))

提示：如果左右数据框中的键相同，只需使用 on。

Left join and ValueError: Wrong number of items passed 55, placement implies 1

Left join and ValueError: Wrong number of items passed 55, placement implies 1

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