How to create an empty numpy array with semi-specified dims?

Question

I am trying to read data from a server like this:

with requests.Session() as s:
    data = {}
    r = s.get('https://something.com' , json = data ).json()
    training_set1 = np.empty([-1,4])
    training_set1[:,0] = r["o"]
    training_set1[:,1] = r["h"]
    training_set1[:,2] = r["l"]
    training_set1[:,3] = r["c"]

But I don't know the length of arrays, so I used -1 then got this error message:

ValueError: negative dimensions are not allowed

How can I fix this code? The response r is a JSON object:

{"t":[1322352000,1322438400], 
 "o":[123,123], 
 "h":[123,123], 
 "l":[123,123], 
 "c":[123,123]}

that I am trying to rearrange it to a numpy array.

Possible duplicate of https://stackoverflow.com/questions/10121926/initialise-numpy-array-of-unknown-length — Teshan Shanuka J, Jun 20 '19 at 05:55

Teshan Shanuka J · Accepted Answer · 2019-06-21T04:01:11.567

1

Numpy arrays have fixed sizes. You cannot initialize a dynamic sized array. What you can do is use a list of lists and later convert the list to a numpy array.

Something like this should work assuming r["x"] is a list. (Untested code)

with requests.Session() as s:
    data = {}
    r = s.get('https://something.com' , json = data ).json()
    t_set1 = []
    t_set1.append(r["o"])
    t_set1.append(r["h"])
    t_set1.append(r["l"])
    t_set1.append(r["c"])
training_set1 = np.array(t_set1)

Edit: Edited for the order "o","h","l",""c after OP edited the question

edited Jun 21 '19 at 04:01

answered Jun 20 '19 at 05:58

Teshan Shanuka J

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It seems the order of data is wrong with using your code. – Hasani Jun 20 '19 at 16:30

score 1 · Answer 2 · answered Jun 20 '19 at 06:09

1

You cannot declare a numpy array with an unknown dimension. But you can declare it in one single operation:

training_set1 = np.array([r["o"], r["o"], r["h"], r["l"]])

or even better:

training_set1 = np.array([r[i] for i in "oohl"])

answered Jun 20 '19 at 06:09

Serge Ballesta

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Why do did you use `oohl` instead of `cohl`? – Hasani Jun 20 '19 at 16:03
@user145959 You edited the question. Initially it was `oohl` and now its `ohlc` – Teshan Shanuka J Jun 21 '19 at 04:02

How to create an empty numpy array with semi-specified dims?

2 Answers2