title: Change Data Type of a Set of Entries in a Data Frame
body: <p>I've imported a csv file with 15 columns and 100,000+ rows into a data frame. One of the columns is 'birth' to indicate the birth year. Within the column 'birth' there are actually 3 different string type formats, those that list the date in the format '02-Aug-34', those that list its format as '29DEC1899', and lastly a blank string format ''.</p>
  
  <p>I've written a script that can sort the types of 'birth' strings and then converts the ones that aren't blank into the datetime format for the given date. I use a loop that iterates through an appropriate list with the row number to replace the data frame 'birth' entry from string to datetime, basically overriding the previous value.</p>
  
  <p>To go through the 100,000+ entries takes about 130 seconds. Is there a more efficient way convert the data types given the 3 different possible cases of input values? Is this completion time (130ish seconds) reasonable?</p>
  
  <p>I'm very new to using pandas.</p>