How to Solve NumPy "TypeError: Field elements must be 2- or 3-tuples, got 1
The TypeError: Field elements must be 2- or 3-tuples, got...
in NumPy arises primarily when attempting to create a structured NumPy array from improperly formatted data.
This guide focuses on how to correctly create NumPy arrays, especially 2D arrays and avoid this common TypeError.
Understanding the Error: Incorrect Array Creation
The error typically occurs when you try to pass multiple separate lists as arguments to numpy.array()
instead of passing a single list containing the lists.
import numpy as np
# Incorrect: TypeError: Field elements must be 2- or 3-tuples, got '1'
try:
arr = np.array([2, 4, 6], [1, 3, 5])
except TypeError as e:
print(e)
Output:
Field elements must be 2- or 3-tuples, got '1'
This error happens because NumPy interprets each list as a field name and each element within the list as field information for constructing structured arrays, which isn't what you wanted in this case.
Creating a 2D NumPy Array Correctly
To fix this, pass a single list of lists to numpy.array()
.
From a List of Lists
This is the most common way to create a 2D NumPy array:
import numpy as np
arr = np.array([[2, 4, 6], [1, 3, 5]])
print(arr)
Output:
[[2 4 6]
[1 3 5]]
The key is to have a single set of square brackets []
enclosing the entire structure.
From a Tuple of Lists
You can also use a tuple to store the sublists:
import numpy as np
arr = np.array(([2, 4, 6], [1, 3, 5]))
print(arr)
Output:
[[2 4 6]
[1 3 5]]
Creating a 1D NumPy Array
To create a one-dimensional array, you have to wrap all of the values in one single set of square brackets:
import numpy as np
arr = np.array([1, 3, 5, 7, 9, 11])
print(arr)
Output:
[ 1 3 5 7 9 11]
Specifying Data Types (dtype)
The numpy.array() function can take dtype
as an argument, which will control the datatype of the items, for example using dtype=float
will set the data type to float.
import numpy as np
arr = np.array([[1, 2, 3], [4, 5, 6]], dtype=float)
print(arr)
print(arr.dtype)
Output:
[[1. 2. 3.]
[4. 5. 6.]]
float64
Conclusion
The TypeError: Field elements must be 2- or 3-tuples, got...
error arises when you incorrectly structure the input to numpy.array()
.
To solve this, ensure you pass a single list (or tuple) containing your rows (which are also lists or tuples).
Pay attention to the use of brackets, and use dtype
to set the desired data type.