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pythonnumpytype-conversion
Meh
Meh

Reputation: 7176

How to convert an array of strings to an array of floats in numpy?

How do I make the following conversion in NumPy?

["1.1", "2.2", "3.2"]  ⟶  [1.1, 2.2, 3.2]

Upvotes: 191

Views: 564951

Answers (6)

cottontail
cottontail

Reputation: 23439

If you have an array that contains invalid values such as an empty string (''), then a straightforward casting would raise an error. If you just want to convert this "problematic" array into a numpy float array and handle the invalid values later, then pandas package has a function (pandas.to_numeric) that sets invalid values to NaN and converts the rest to float.

import pandas as pd

a = np.array(["1.1", "2.2"], float)      # OK

lst = ["1.1", "2.2", "3.2.", ""]
a = np.array(lst, float)                 # ValueError: could not convert string to float: '3.2.'
a = pd.to_numeric(lst, errors='coerce')  # array([1.1, 2.2, nan, nan])

Upvotes: 0

Mayank Soni
Mayank Soni

Reputation: 91

You can use np.array() with dtype = float:

import numpy as np

x = ["1.1", "2.2", "3.2"]
y = np.array(x,dtype=float)

Output:

array([1.1, 2.2, 3.2])

Upvotes: 6

Herpes Free Engineer
Herpes Free Engineer

Reputation: 2682

Another option might be numpy.asarray:

import numpy as np
a = ["1.1", "2.2", "3.2"]
b = np.asarray(a, dtype=float)

print(a, type(a), type(a[0]))
print(b, type(b), type(b[0]))

resulting in:

['1.1', '2.2', '3.2'] <class 'list'> <class 'str'>
[1.1 2.2 3.2] <class 'numpy.ndarray'> <class 'numpy.float64'>

Upvotes: 21

Thomio
Thomio

Reputation: 1433

If you have (or create) a single string, you can use np.fromstring:

import numpy as np
x = ["1.1", "2.2", "3.2"]
x = ','.join(x)
x = np.fromstring( x, dtype=np.float, sep=',' )

Note, x = ','.join(x) transforms the x array to string '1.1, 2.2, 3.2'. If you read a line from a txt file, each line will be already a string.

Upvotes: 7

pradeep bisht
pradeep bisht

Reputation: 66

You can use this as well 

import numpy as np
x=np.array(['1.1', '2.2', '3.3'])
x=np.asfarray(x,float)

Upvotes: 5

Joe Kington
Joe Kington

Reputation: 284890

Well, if you're reading the data in as a list, just do np.array(map(float, list_of_strings)) (or equivalently, use a list comprehension). (In Python 3, you'll need to call list on the map return value if you use map, since map returns an iterator now.)

However, if it's already a numpy array of strings, there's a better way. Use astype().

import numpy as np
x = np.array(['1.1', '2.2', '3.3'])
y = x.astype(np.float)

Upvotes: 269

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