python - When using a pandas dataframe, how do I add column if does not exist?

Question

I'm new to using pandas and am writing a script where I read in a dataframe and then do some computation on some of the columns.

Sometimes I will have the column called "Met":

df = pd.read_csv(File, 
  sep='', 
  compression='gzip', 
  header=0, 
  names=["Chrom", "Site", "coverage", "Met"]
)

Other times I will have:

df = pd.read_csv(File, 
  sep='', 
  compression='gzip', 
  header=0, 
  names=["Chrom", "Site", "coverage", "freqC"]
)

I need to do some computation with the "Met" column so if it isn't present I will need to calculate it using:

df['Met'] = df['freqC'] * df['coverage'] 

is there a way to check if the "Met" column is present in the dataframe, and if not add it?

question from:https://stackoverflow.com/questions/25896453/when-using-a-pandas-dataframe-how-do-i-add-column-if-does-not-exist

Answer 1

You check it like this:

if 'Met' not in df:
    df['Met'] = df['freqC'] * df['coverage']