extracting values by using dictionary key

[InceptionWoznicki]

Hi Guys,

I have text file having two columns: 1) column 1 is in the format yyyy-mm-dd and 2) column 2 is precipitation.

Objective: to extract original value of precipitation from column 2 only for month April, May, june, July, and August (4,5,6,7,8).

Procedure: Used line.split to extract only mm from yyyy-mm-dd format from column-1.

• made dictionary to get month and precipitation value.
• using for k,v in dct.items() and then using a if statement to extract the corresponding month precipitation value from dictionary

Problem: I can successfully print k,v (month and precipitation) from dictionary items. However, when I am using a if statement to extract the specific month's precipitation value, I am getting blank array. I was wondering can I use .append to get precipitation in (1.8,2.1,3.3) format.

Code:

file1 = open("test.txt","r")  Growing=[] Intermediate=[] Dormant=[]  for line in file1:     line2 = line.split()     WQ = line2[1]     month = line2[0].split("-")[1]     dct1={month:WQ}     for k,v in dct1.items():         if (k ==4 or k==5 or k==6 or k==7 or k==8):             Growing.append(dct1 )     print Growing

[XanderBakker · Accepted solution]

Using the attached sample file and the code below I obtained a list of precipitation values:

infile = r"D:\Xander\txt\precip.txt"
sep = "\t" # example TAB as seperator

lst_months = [4, 5, 6, 7, 8]
growing = []
header = 1
i = 0
with open(infile,"r") as f:
    for line in f:
        i += 1
        if i > header:
            line = line.strip("\n")
            data = line.split(sep)
            if len(data) == 2:
                print data
                date = data[0]
                prec = float(data[1])
                month = int(date.split("-")[1])
                if month in lst_months:
                    growing.append(prec)

print growing

Kind regards, Xander

[InceptionWoznicki]

Hi Xander,

Thanks a lot for your help! I was stuck and it really helped me.Yeah, the code is working perfect. Appreciate it. Have a good one!

Sean

[XanderBakker]

Hi Sean, you´re welcome. Can you mark the question as answered?

Kind regards, Xander

[InceptionWoznicki]

How do I mark as answered. I looked at and found a link called as mark as helpful and did that. Is that what you wanted me to do?

[XanderBakker]

There should be a star "Correct Answer" that you can press next to the post that answered you question.

[InceptionWoznicki]

I think I marked as answer  now. Thank you!

[XanderBakker]

Yes you did. Thanks!

[InceptionWoznicki]

Hi Xander,

Just a silly question. I want to extract the corresponding date of the precip along with the precip value. For that, I added one line code: growing.append(float(date)) after growing.append(prec) in your code.

However, I got this error:"ValueError: invalid literal for float(): 2007-05-07". Do you mind to look at it?

Thank you very much for your time and help!

Sean

[XanderBakker]

Hi Sean,

Basically the error is telling you that the date (2007-05-07) is not a float (decimal value). The other thing is that your code will result in a list that holds a precipitation value, a date, a precipitation value, a date, etc. It would probably be more appropriate to work with a nested list like this:

date = data[0]
prec = float(data[1])
lst_date_prec = [date, prec]
month = int(date.split("-")[1])
if month in lst_months:
    growing.append(lst_date_prec)

This results i a list where each item contains a list of a precipitation value and the corresponding date. It really depends on what you want to do with the list...

Kind regards, Xander