Logarithmic operation on pandas dataframe-Key value error

Question

I have a data frame as shown below.it's name is 'df_thd_funct' .I need to apply logarithmic equation on xvalue columns and need to create a new column.Below is my code.

df_thd_funct['sensi'] = 20*(np.log(df_thd_funct.xvalues/1.44)) 

xvalues SFM_376_1.62_-40    
0.0189     0.0190                       
0.0200     0.0187               
0.0225     0.0167              
0.0239     0.0191

The error I am getting is given below. What am I missing?

My complete code is given below.

df_thd_funct = pd.read_csv("A2_THD_Ratio_Stepped_Sweep_Corners_PVT_lab01.txt",delim_whitespace=True,index_col=False)
df_thd_funct.set_index('xvalues', inplace=True)
check_for_nan = df_thd_funct.isnull().values.any()
df_thd_funct = df_thd_funct.T
print (check_for_nan)
df_thd_funct.head()

After running df_thd_funct['sensi'] = df_thd_funct['xvalues'].apply(lambda x: 20*(np.log(x/1.44)))

The new error obtained is given below.

always put FULL error message (starting at word "Traceback") in question (not in comments) as text (not screenshot, not link to external portal). There are other useful information in the full error/traceback. — furas
– furas, Commented Oct 7, 2022 at 12:55
Thnak you ,but I am getting this error "KeyError: 'xvalues'" — Confused
– Confused, Commented Oct 11, 2022 at 7:26

imburningbabe · Accepted Answer · 2022-10-07 09:28:17Z

1

You can't give np.log a pd.Series as argument, you have to use lambda function:

import pandas as pd

df = pd.DataFrame({'xvalues':[0.0189,0.0200,0.0225,0.0239]})

df['sensi'] = df['xvalues'].apply(lambda x: 20*(np.log(x/1.44)))

Output:

   xvalues      sensi
0   0.0189 -86.664729
1   0.0200 -85.533322
2   0.0225 -83.177662
3   0.0239 -81.970399

answered Oct 7, 2022 at 9:28

imburningbabe

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4 Comments

Confused Over a year ago

Thank you. I updated my question which shows how I read the data frame and the new error obtained after running the code df['sensi'] = df['xvalues'].apply(lambda x: 20*(np.log(x/1.44)))

imburningbabe Over a year ago

Because the lambda function take the 'xvalues' column as argument, but you set that column as index

Confused Over a year ago

Correct xvalues is my index. Unfortunately I can't change that.May I know how to solve this

imburningbabe Over a year ago

Ypu can just perform the log calc and THEN set 'xvalues' as index

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