大熊猫合并返回NaN？(Pandas Merge returning NaN?)

 我有2个数据框： 
 
 DF1 = 
 
State           Code
Alabama         AL
Alaska          AK
American Samoa  AS
Arizona         AZ
Arkansas        AR
 
 DF2 = 
 
State            PREVAILING_WAGE
CALIFORNIA       102170.0
DELAWARE         97531.0
SOUTH CAROLINA   96824.0
WASHINGTON       89586.0
OREGON           88234.0
 
 现在当我尝试合并时，如果他们使用： 
 
df1.merge(df2,left_on='State',right_on='State',how='left')
 
 我在合并表中获得NaN值，如下所示： 
 
State          PREVAILING_WAGE   Code
CALIFORNIA     102170.0          NaN
DELAWARE       97531.0           NaN
SOUTH CAROLINA 96824.0           NaN
WASHINGTON     89586.0           NaN
OREGON         88234.0           NaN
 
 我也检查了dtypes，并且它们都是对象或str。 我该如何解决这个问题？ 
 
 谢谢 
 
 编辑 ：dataframes包含所有的状态名称，所以他们有共同的东西来匹配。 

I have 2 dataframes:
 
df1=
 
State           Code
Alabama         AL
Alaska          AK
American Samoa  AS
Arizona         AZ
Arkansas        AR
 
df2=
 
State            PREVAILING_WAGE
CALIFORNIA       102170.0
DELAWARE         97531.0
SOUTH CAROLINA   96824.0
WASHINGTON       89586.0
OREGON           88234.0
 
Now when I try to merge both if them using:
 
df1.merge(df2,left_on='State',right_on='State',how='left')
 
I get NaN values in the merged table like this:
 
State          PREVAILING_WAGE   Code
CALIFORNIA     102170.0          NaN
DELAWARE       97531.0           NaN
SOUTH CAROLINA 96824.0           NaN
WASHINGTON     89586.0           NaN
OREGON         88234.0           NaN
 
I checked the dtypes too, and both of them are objects or str. How do I solve this?
 
Thanks
 
EDIT: The dataframes contain all states names, so they have common stuff to match.

原文：https://stackoverflow.com/questions/49324970