Converting Z-Score to Percentile in Python

gistfile1.txt

def zptile(z_score):
    return .5 * (math.erf(z_score / 2 ** .5) + 1)

zptile(0.95)

# excel says: 0.8289438737

0.8289438736915181

via: http://stackoverflow.com/questions/2782284/function-to-convert-a-z-score-into-a-percentage

To get this to work in a dataframe you need to use the APPLY function

df["PTILE"]=df["ZSCORE"].apply(zptile)

df["PTILE"]=zptile(df["ZSCORE"]) will not work...

see: http://stackoverflow.com/questions/23748842/understanding-math-errors-in-pandas-dataframes


To iterate over a slice of columns and perform the calculation on each one -- in this case i'm starting with the column 'pop' and taking every column to the right, iterating through, creating a new zscore percentile column called columnname_p:

for col in df.ix[:,'pop':]:
    df[col+"_p"]=((df[col] - df[col].mean())/df[col].std(ddof=0)).apply(zptile)*100

use lambda to iterate over df in single code