Equivalent of R/ifelse in Python/Pandas? Compare string columns?

Question

My goal is comparing between two columns and add the result column. R uses ifelse but I need to know pandas's way.

R

> head(mau.payment)   log_month user_id install_month payment 1   2013-06       1       2013-04       0 2   2013-06       2       2013-04       0 3   2013-06       3       2013-04   14994  > mau.payment$user.type <-ifelse(mau.payment$install_month == mau.payment$log_month, "install", "existing") > head(mau.payment)   log_month user_id install_month payment user.type 1   2013-06       1       2013-04       0  existing 2   2013-06       2       2013-04       0  existing 3   2013-06       3       2013-04   14994  existing 4   2013-06       4       2013-04       0  existing 5   2013-06       6       2013-04       0  existing 6   2013-06       7       2013-04       0  existing 

Pandas

>>> maupayment user_id  log_month  install_month 1        2013-06    2013-04              0          2013-07    2013-04              0 2        2013-06    2013-04              0 3        2013-06    2013-04          14994 

I tried some cases but did not work. It seems that string comparison does not work.

>>>np.where(maupayment['log_month'] == maupayment['install_month'], 'install', 'existing')  TypeError: 'str' object cannot be interpreted as an integer  

Could you help me please?

---

Pandas and numpy version.

>>> pd.version.version '0.16.2' >>> np.version.full_version '1.9.2' 

---

After update the versions, it worked!

>>> np.where(maupayment['log_month'] == maupayment['install_month'], 'install', 'existing') array(['existing', 'install', 'existing', ..., 'install', 'install',        'install'],        dtype='<U8') 

Answer 1

You have to upgrade pandas to last version, because in version 0.17.1 it works very well.

Sample (first value in column install_month is changed for matching):

print maupayment   log_month  user_id install_month  payment 1   2013-06        1       2013-06        0 2   2013-06        2       2013-04        0 3   2013-06        3       2013-04    14994  print np.where(maupayment['log_month'] == maupayment['install_month'], 'install', 'existing') ['install' 'existing' 'existing']