I would like to create a new column with the number of time a string appears in another column.

Example:
The new column would count the number of times "X" appears in the caption column.

```
col1    caption                 new_column
a       "hello X, welcome!"      1 
b       "Beautiful day"          0
c       "X or x. Box."           1
d       "Xina is a cool name. X" 2

```