Conversion string values to float/int
Dictionary = {"Orange fruit" :1 ,"Cherry fruit" :2,......,"PineApple fruit":10}
MyDataFrame['Number Column'] = MyDataFrame['String Column'].apply(Dictionary.get)

In the figure attached , String Column consists Fruit names 
                                     Number Column consists corresponding numbers for fruit names

Only 128 rows are converted to corresponding numbers as assigned in Dictionary.
and then all rows in "Number Column " are not assigned and are empty(NaN)

Note: There are few values in first 125 rows which are not converted to corresponding numbers.

![selection_001](https://cloud.githubusercontent.com/assets/6937958/3160862/d6588b68-eb25-11e3-8b04-5cbf88fb01ed.png)
