Select entry from array given another value

Question

I have a text file with the format (date, time, resistance):

12/11/2013  13:20:38    28.321930E+3
...         ...             ...

I need to extract the value of resistance (third column) from every 6 seconds after the first data entry. To start I wanted to import the text file using:

date, time, resistance = loadtxt('Thermometers.txt', unpack=True, usecols=[0,1,2])

However before I've hardly begun my program, I get the error:

ValueError: invalid literal for float(): 12/11/2013

-ALSO-

I am not sure how to also iterate through time given that the date changes as it's an over-night data run. Elegant solutions to my problem(s) would be much appreciated.

Answer 1

I think this code will do what you want to do. And also, you don't have to worry about the overnight data and changing date since this converts it to datetime object.

    import datetime

    filtered_data=[]

    my_data=open(my_file,'r')
    for line in my_data:

        data_arr=line.split()
        dte=data_arr[0].split("/") r
        tme=data_arr[1].split(":") 
        new_date=datetime.datetime((int(dte[2]),int(dte[0]),int(dte[1]),
                                    int(tme[0]),int(tme[1]),int(tme[2]))

        if filtered_data==[]:
           filtered_data.append(data_arr)

        else:
           if (new_date-old_date).seconds==6:
                filtered_data.append(data_arr)

        old_date=new_date

This will give you a list where the items are filtered as per your situation ( in every 6 seconds). Now if you just want the array of your resistance which are distributed at 6 seconds interval, using simple loop or list comprehension like below will suffice:

R_in_six_sec_interval=[R[2] for R in filtered_data]