return specific values from an array

Question

I have an array like this

array([['Weather1', 428, '74827'],
 ['weather1', 429, '74828'],
 ['weather1', 409, '74808'],
 ['weather2', 11553, '76568'],
 ['weather2', 11573, '76574'],

I want to return only the [2] values into a new array group by the values in [0]

Final outcome:

array([['74827', '74828', '74808'],['76568', '76574']]

Any ideas?

• xavi: My question has a huge overlap with these question stackoverflow.com/questions/38013778/…

Answer 1

Yes, you can do this:

array = [
 ['Weather1', 428, '74827'],
 ['weather1', 429, '74828'],
 ['weather1', 409, '74808'],
 ['weather2', 11553, '76568'],
 ['weather2', 11573, '76574']
]
read_data = [] # stores Weather1, Weather2 etc. as we read that
final_array = [] # stores final arrays
# stores data for weather1, then clears it out and
# then stores data for weather2, and so on...
sub_array = [] 
# read each item of array
for x in array:
 # e.g. for first row, is Weather1 already read?
 # No, it's not read
 if x[0].lower() not in read_data:
 # when you reach weather 2 and hit this statement,
 # sub_array will have data from weather1. So, if you find
 # sub_array with data, it is time to add it to the final_array
 # and start fresh with the sub_array
 if len(sub_array) > 0:
 final_array.append(sub_array)
 sub_array = [x[2]]
 # if sub_array is empty, just add data to it
 else:
 sub_array.append(x[2])
 
 # make sure that read_data contains the item you read
 read_data.append(x[0].lower())
 # if weather1 has been read already, just add item to sub_array
 else:
 sub_array.append(x[2])
# After you are done reading all the lines, sub_array may have data in it
# if so, add to the final alrray
if len(sub_array) > 0:
 final_array.append(sub_array)
print(final_array)

Result: [['74827', '74828', '74808'], ['76568', '76574']]

Assumption: Your data is sequential. That means, weather1 data goes on for a few lines and then weather2 (or something not weather1) goes on for a few lines and so on.

• Richard Valenz: Contribution: In case the data was not sequential, you could also sort your data on "weather...", then you will have all weather1, weather2, etc together so that you can define a separation of groups by the index in which the weather has changed.
• xavi: Why i get back IndexError: index 2 is out of bounds for axis 0 with size 2
• zedfoxus: @xavi how does you data look like? Does any of your array not have the last string like '74827'?
• xavi: just a kernel restart solves the problem. Thanks
• zedfoxus: @RichardValenz you said it so well. If x[0] is not sequential, just sort the data. Thank you!