Accessing fields by name in NumPy - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a structured array in NumPy?

A structured array is a NumPy array that can hold different data types in named fields, like columns in a table.

beginner

How do you access a field named 'age' in a structured NumPy array called 'data'?

You use data['age'] to get all values in the 'age' field.

beginner

Why is accessing fields by name useful in NumPy structured arrays?

It lets you work with specific columns easily without affecting other data, similar to selecting a column in a spreadsheet.

intermediate

Can you assign new values to a field in a NumPy structured array? How?

Yes, by using data['field_name'] = new_values, you can update the values in that field.

intermediate

What happens if you try to access a field name that does not exist in a NumPy structured array?

NumPy raises a ValueError because the field name is not found in the array's dtype.

How do you access the 'height' field in a structured NumPy array named 'people'?

A people.get('height')

B people['height']

C people.height()

D people.height

In NumPy structured arrays, fields are accessed using square brackets and the field name as a string.

What type of object is returned when you access a field by name in a structured array?

A A NumPy array of the field's values

B A Python list

C A scalar value

D A dictionary

Accessing a field returns a NumPy array containing all values for that field.

If 'data' is a structured array, what does data['age'] = 30 do?

A Raises an error

B Deletes the 'age' field

C Adds a new field 'age' with value 30

D Sets all 'age' values to 30

Assigning a value to a field updates all entries in that field.

What error occurs if you try to access a non-existent field in a structured array?

A ValueError

B IndexError

C TypeError

D KeyError

Accessing a missing field raises a ValueError.

Which of these is NOT a valid way to access fields in a NumPy structured array?

A array.field

B array['field']

C array.get('field')

D array['field_name']

NumPy structured arrays do not have a .get() method for accessing fields. Use array['field'] or array.field.

Explain how to access and update a field named 'score' in a NumPy structured array.

Think about how you select columns in a table.

Describe what happens if you try to access a field that does not exist in a structured array.

What error do you get when a key is missing in a dictionary?