creating a numpy array in a loop

Question

I want to create a numpy array by parsing a .txt file. The .txt file consists of features of iris flowers seperated by commas. every line is has one flower example with 5 data seperated with 4 commas. first 4 number is features and the last one is the name. I parse the .txt in a loop and want to append (using numpy.append probably) every lines parsed data into a numpy array called feature_table.

heres the code;

import numpy as np
iris_data = open("iris_data.txt", "r")
for line in iris_data:
    currentline = line.split(",")
    #iris_data_parsed = (currentline[0] + " , " + currentline[3] + " , " + currentline[4])
    #sepal_length = numpy.array(currentline[0])
    #petal_width = numpy.array(currentline[3])
    #iris_names = numpy.array(currentline[4])
    feature_table = np.array([currentline[0]],[currentline[3]],[currentline[4]])
    print (feature_table)
    print(feature_table.shape)

so I want to create a numpy array using only first, fourth and fifth data in every line but I can't make it work as I want to. tried reading numpy docs but couldn't understand it.

You're continously overwriting the same variable, so you get an array with just 3 elements. — 9769953
– 9769953, Commented Feb 19, 2019 at 12:11
Depending on your ultimate goal, you may be better off using numpy.loadtxt, pandas (which has a read_sv() function that reads the whole file into a table a.k.a. a Dataframe), or even scikit-learn, which uses the iris data sets in lots of examples. — 9769953
– 9769953, Commented Feb 19, 2019 at 12:13
@9769953 you are right, but I dont even get an array with 3 elements, I get ValueError: only 2 non-keyword arguments accepted. — Emre Unsal
– Emre Unsal, Commented Feb 19, 2019 at 12:13
answer by @Alexander Rossa fixed that. now I just have to create a numpy array outside of the loop and update it every line. thanks — Emre Unsal
– Emre Unsal, Commented Feb 19, 2019 at 12:19

Alexander Rossa · Accepted Answer · 2019-02-19 12:15:08Z

2

While the people in the comments are right in that you are not persisting your data anywhere, your problem, I assume, is incorrect np.array construction. You should enclose all of the arguments in a list like this:

feature_table = np.array([currentline[0],currentline[3],currentline[4]])

And get rid of redundant [ and ] around the arguments.

See the official documentation for more examples. Basically all of the input data needs to be grouped/separated to be only 1 argument as Python will consider the other arguemnts as different positional arguments.

answered Feb 19, 2019 at 12:15

Alexander Rossa

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1 Comment

Emre Unsal Over a year ago

Thanks for the swift answer. Now I just have to create a numpy array outside of the loop and update it every line.

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