get first 2 characters of each index in array in python

Question

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I am trying to access the first two letters of each index in a numpy array in python: I have read previous forum of the error "'int' object is not subscriptable , I know it;s not a string, but for my work it's better to be numpy.array or if anyone suggest me with another thing, please help,

Here is my code:

import numpy as np
import os
import os.path
with open('trial.dat', 'r') as f:
     data = f.readlines()
     data = [(d+' ')[:d.find('#')].rstrip() for d in data]

x=len(data[0])
x_1=eval(data[0])
y=np.concatenate(x_1)
print(type(y))
for i in range (x):
    if y[i[:2]]=='IS': # expected to be IS andso on.depened on the index
         print('ok-CHOICE ONE ')
elif y[i[:2]]=='AT':  
     print('NOTok ')
else:
     print()

Data to be used in the .dat file:

[["IS-2","AT-3","IS-4"]]                # TYPE OF GN

Side note: eval is very dangerous, but your data looks like valid JSON (when the comment is removed). You could use json.loads instead. — Tim Roberts
– Tim Roberts, Commented Nov 15, 2021 at 18:30

hpaulj · Accepted Answer · 2021-11-15 20:02:22Z

1

You can't efficiently slice string elements with [:2], but you can use astype to truncate the strings:

In [306]: alist = ["IS-2","AT-3","IS-4"]
In [307]: np.array(alist)
Out[307]: array(['IS-2', 'AT-3', 'IS-4'], dtype='<U4')

In [309]: np.array(alist).astype('U2')
Out[309]: array(['IS', 'AT', 'IS'], dtype='<U2')

The resulting array could be tested against 'IS' etc:

In [310]: np.array(alist).astype('U2')=='IS'
Out[310]: array([ True, False,  True])
In [311]: np.array(alist).astype('U2')=='AT'
Out[311]: array([False,  True, False])

Using two where steps:

In [312]: np.where(Out[309]=='IS', "ok-CHOICE ONE", Out[307])
Out[312]: array(['ok-CHOICE ONE', 'AT-3', 'ok-CHOICE ONE'], dtype='<U13')
In [313]: np.where(Out[309]=='AT', "NOTok", Out[312])
Out[313]: array(['ok-CHOICE ONE', 'NOTok', 'ok-CHOICE ONE'], dtype='<U13')

np.select could probably used as well.

answered Nov 15, 2021 at 20:02

hpaulj

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1 Comment

msci Over a year ago

Thank you so much, would it be possible also to get the last two characters, (which are numbers (integer in that case ??) Thanks again

not_speshal · Accepted Answer · 2021-11-15 18:40:14Z

0

Try:

with open('trial.dat') as f:
    line = f.readline() #readline (singular) since the file has only one line
    data = [word.strip('"') for word in line.split("#")[0].strip(" []").split(",")]

for string in data:
    if string.startswith("IS"):
        print(f"{string}: ok-CHOICE ONE")
    elif string.startswith("AT"):
        print(f"{string}: NOT ok")
    else:
        print(f"{string}: Other")

Output:

IS-2: ok-CHOICE ONE
AT-3: NOT ok
IS-4: ok-CHOICE ONE

answered Nov 15, 2021 at 18:40

not_speshal

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1 Comment

msci Over a year ago

Can not we do like my earlier code, as the file will contain other lines , and do not wanna change read approach ?? Also, I am wondering not other way to read index inside index as I wanna

Tim Roberts · Accepted Answer · 2021-11-15 19:02:45Z

0

Consider this as a starting point. Notice the simple change to handle multiple lines.

import json

data = """\
[["IS-2","AT-3","IS-4"]]                    # TYPE OF GN
[["IS-2","AT-3","IS-4"]]                    # TYPE OF GN
[["IS-2","AT-3","IS-4"]]                    # TYPE OF GN
[["IS-2","AT-3","IS-4"]]                    # TYPE OF GN"""

for row in data.splitlines():
    row  = row.partition(' ')[0]
    row = json.loads( row)

    for i in row[0]:
        if i[:2] == "IS":
            print(i,"OK" )
        elif i[:2] == 'AT':
            print(i, "NOT OK")
        else:
            print(i, "unknown")

Output:

IS-2 OK
AT-3 NOT OK
IS-4 OK
IS-2 OK
AT-3 NOT OK
IS-4 OK
IS-2 OK
AT-3 NOT OK
IS-4 OK

edited Nov 15, 2021 at 19:02

answered Nov 15, 2021 at 18:33

Tim Roberts

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2 Comments

msci Over a year ago

Thank you very much for your feedback, mmm... I just would prefer to use numpy as I have a lot of other inputs and need them to be an array ? Also, in the above mentioned code, i got the following error: line 4, in <module> data = data.partition(' ')[0] AttributeError: 'list' object has no attribute 'partition'

Tim Roberts Over a year ago

You have string data. numpy doesn't really help you here. And clearly, if you are running through a LIST of such lines, then you need an outer loop. for row in my_data: / for i in row[0].

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