Assigning content of a pandas DataFrame cell based on some condition without using loops

I have a pandas DataFrame df with the following content:

Serial N       voltage       current
   B              10            nan
   B              10            nan
   C              12            nan
   D              40            nan
   .               .             .
   AB             12            nan

I also have the following dictionary which contains the current values as following (my key here is the serial number):

my_dict={A:0.6,B:0.2, ...,AB:0.2}

I would like to store the content of my dictionary into the dataFrame column "current" based on the dictionary. I can have multiple serial number in the dataFrame df with the same value. I would like to do so without using loops if possible. I tried this:

for k,v in my_dict.items():
   if df["Serial N"]==k:           
       df["current"]=v

But it does not to work, Because I do not have the position of the rows (I can have several Serial number with same value; example: B in the Serial N column) where the condition is satisfied. How can I do this without a loop?

Answers


You can use map:

print df
  Serial N  voltage  current
0        B       10      NaN
1        B       10      NaN
2        C       12      NaN
3        D       40      NaN
4       AB       12      NaN

my_dict={"A":0.6,"B":0.2,"AB":0.2}
print my_dict
{'A': 0.6, 'B': 0.2, 'AB': 0.2}

df['current'] =  df['Serial N'].map(my_dict)
print df
  Serial N  voltage  current
0        B       10      0.2
1        B       10      0.2
2        C       12      NaN
3        D       40      NaN
4       AB       12      0.2

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