Solved: ValueError: could not convert string to float: ‘’

Python and Pandas

When using Python and Pandas to load and manipulate data it is almost certain that at some point in time you will have to convert data to make it usable to the wider project.

When loading data, in our example originating from a csv file, into a pandas dataframe you will have the data represented as an object type. Even though initially usable there is a common need to transform this into a more usable format, for example a float64 format.

Two options to transform from object to float64 are outlined below

pandas.DataFrame.astype

This is used to cast a pandas object to a specified dtype. In our example we try to transform this into a float64 as show in the example below where we try to transform “avg_use” into a float.

df['avg_use']=df['avg_use'].astype(float)

In general this method works quite well, the exception to this is that you might run into a ValueError as shown below. This commonly is the case if your dataset is not clean and “avg_use” contains values that are not able to be converted to a float. Even though a dataset should be clean, obviously, reality shows that datasets are not always as clean as we would hope for.

ValueError: could not convert string to float: ‘’