Question: I need help to make the snippet below. I need to merge two files and performs computation on matched lines I have oldFile.txt which contains old data and newFile.txt with an updated sets of data. I need to to update the oldFile.txt based on the data in the newFile.txt and compute the changes in percentage. Any idea will be very helpful. Thanks in advance from collections import defaultdict num = 0 data=defaultdict(int) with open("newFile.txt", encoding='utf8', errors='ignore') as f: for line in f: grp, pname, cnt, cat = line.split(maxsplit=3) data[(pname.strip(),cat.replace('\n','').strip(),grp,cat)]+=int(cnt) sorteddata = sorted([[k[0],v,k[1],k[2]] for k,v in data.items()], key=lambda x:x[1], reverse=True) for subl in sorteddata[:10]: num += 1 line = " ".join(map(str, subl)) print ("{:>5} -> {:>}".format(str(num), line)) with open("oldFile.txt", 'a', encoding='utf8', errors='ignore') as l: l.write(" ".join(map(str, subl)) + '\n')  oldFile.txt  #col1 #col2 #col3 #col4 1,396 c15e89f2149bcc0cbd5fb204 4 HUH_Token (HUH) 279 9e4d81c8fc15870b15aef8dc 3 BABY BNB (BBNB) 231 31b5c07636dab8f0909dbd2d 6 Buff Unicorn (BUFFUN...) 438 1c6bc8e962427deb4106ae06 8 Charge (Charge) 2,739 6ea059a29eccecee4e250414 2 MAXIMACASH (MAXCAS...)  newFile.txt #-- updated data with additional lines not found in oldFile.txt  #col1 #col2 #col3 #col4 8,739 6ea059a29eccecee4e250414 60 MAXIMACASH (MAXCAS...) 138 1c6bc8e962427deb4106ae06 50 Charge (Charge) 860 31b5c07636dab8f0909dbd2d 40 Buff Unicorn (BUFFUN...) 200 9e4d81c8fc15870b15aef8dc 30 BABY BNB (BBNB) #-- not found in the oldFile.txt 20 5esdsds2sd15870b15aef8dc 30 CharliesAngel (CA) 1,560 c15e89f2149bcc0cbd5fb204 20 HUH_Token (HUH)  Need Improvement: #-- With additional columns (col5, col6) and sorted based on (col3) values  #col1 #col2 #col3 #col4 #col5 (oldFile-newFile) #col6 (oldFile-newFile) 8,739 6ea059a29eccecee4e250414 62 MAXIMACASH (MAXCAS...) 2900.00 % (col3 2-60) 219.06 % (col1 2,739-8,739) 138 1c6bc8e962427deb4106ae06 58 Charge (Charge) 625.00 % (col3 8-50) -68.49 % (col1 438-138) 860 31b5c07636dab8f0909dbd2d 46 Buff Unicorn (BUFFUN...) 566.67 % (col3 6-40) 272.29 % (col1 231-860) 200 9e4d81c8fc15870b15aef8dc 33 BABY BNB (BBNB) 900.00 % (col3 3-30) -28.32 % (col1 279-200) 20 5esdsds2sd15870b15aef8dc 30 CharliesAngel (CA) 0.00 % (col3 0-30) 20.00 % (col1 0-20) 1,560 c15e89f2149bcc0cbd5fb204 24 HUH_Token (HUH) 400.00 % (col3 4-20) 11.75 % (col1 1,396-1,560) 

Answer: Here is a sample code to output what you need. I use the formula below to calculate pct change. percentage_change = 100*(new-old)/old If old is 0 it is changed to 1 to avoid division by zero error. import pandas as pd def read_file(fn): """ Read file fn and convert data into a dict of dict. data = {pname1: {grp: grp1, pname: pname1, cnt: cnt1, cat: cat1}, pname2: {gpr: grp2, ...} ...} """ data = {} with open(fn, 'r') as f: for lines in f: line = lines.rstrip() grp, pname, cnt, cat = line.split(maxsplit=3) data.update({pname: {'grp': float(grp.replace(',', '')), 'pname': pname, 'cnt': int(cnt), 'cat': cat}}) return data def process_data(oldfn, newfn): """ Read old and new files, update the old file based on new file. Save output to text, and csv files. """ # Get old and new data in dict. old = read_file(oldfn) new = read_file(newfn) # Update old data based on new data u_data = {} for ko, vo in old.items(): if ko in new: n = new[ko] # Update cnt. old_cnt = vo['cnt'] new_cnt = n['cnt'] u_cnt = old_cnt + new_cnt # cnt change, if old is zero we set it to 1 to avoid division by zero error. tmp_old_cnt = 1 if old_cnt == 0 else old_cnt cnt_change = 100 * (new_cnt - tmp_old_cnt) / tmp_old_cnt # grp change old_grp = vo['grp'] new_grp = n['grp'] grp_change = 100 * (new_grp - old_grp) / old_grp u_data.update({ko: {'grp': n['grp'], 'pname': n['pname'], 'cnt': u_cnt, 'cat': n['cat'], 'cnt_change%': round(cnt_change, 2), 'grp_change%': round(grp_change, 2)}}) # add new data to u_data, that is not in old data for kn, vn in new.items(): if kn not in old: # Since this is new item its old cnt is zero, we set it to 1 to avoid division by zero error. old_cnt = 1 new_cnt = vn['cnt'] cnt_change = 100 * (new_cnt - old_cnt) / old_cnt # grp change is similar to cnt change old_grp = 1 new_grp = vn['grp'] grp_change = 100 * (new_grp - old_grp) / old_grp # Update new columns. vn.update({'cnt_change%': round(cnt_change, 2), 'grp_change%': round(grp_change, 2)}) u_data.update({kn: vn}) # Create new data mydata list from u_data, and only extract the dict value. mydata = [] for _, v in u_data.items(): mydata.append(v) # Convert mydata into pandas dataframe to easier manage the data. df = pd.DataFrame(mydata) df = df.sort_values(by=['cnt'], ascending=False) # sort on cnt column # Save to csv file. df.to_csv('output.csv', index=False) # Save to text file. with open('output.txt', 'w') as w: w.write(f'{df.to_string(index=False)}') # Print in console. print(df.to_string(index=False)) # Start oldfn = 'F:/Tmp/oldFile.txt' newfn = 'F:/Tmp/newFile.txt' process_data(oldfn, newfn)  Console output:  grp pname cnt cat cnt_change% grp_change% 8739.0 6ea059a29eccecee4e250414 62 MAXIMACASH (MAXCAS...) 2900.00 219.06 138.0 1c6bc8e962427deb4106ae06 58 Charge (Charge) 525.00 -68.49 860.0 31b5c07636dab8f0909dbd2d 46 Buff Unicorn (BUFFUN...) 566.67 272.29 200.0 9e4d81c8fc15870b15aef8dc 33 BABY BNB (BBNB) 900.00 -28.32 20.0 5esdsds2sd15870b15aef8dc 30 CharliesAngel (CA) 2900.00 1900.00 1560.0 c15e89f2149bcc0cbd5fb204 24 HUH_Token (HUH) 400.00 11.75  text output:  grp pname cnt cat cnt_change% grp_change% 8739.0 6ea059a29eccecee4e250414 62 MAXIMACASH (MAXCAS...) 2900.00 219.06 138.0 1c6bc8e962427deb4106ae06 58 Charge (Charge) 525.00 -68.49 860.0 31b5c07636dab8f0909dbd2d 46 Buff Unicorn (BUFFUN...) 566.67 272.29 200.0 9e4d81c8fc15870b15aef8dc 33 BABY BNB (BBNB) 900.00 -28.32 20.0 5esdsds2sd15870b15aef8dc 30 CharliesAngel (CA) 2900.00 1900.00 1560.0 c15e89f2149bcc0cbd5fb204 24 HUH_Token (HUH) 400.00 11.75  csv output: grp,pname,cnt,cat,cnt_change%,grp_change% 8739.0,6ea059a29eccecee4e250414,62,MAXIMACASH (MAXCAS...),2900.0,219.06 138.0,1c6bc8e962427deb4106ae06,58,Charge (Charge),525.0,-68.49 860.0,31b5c07636dab8f0909dbd2d,46,Buff Unicorn (BUFFUN...),566.67,272.29 200.0,9e4d81c8fc15870b15aef8dc,33,BABY BNB (BBNB),900.0,-28.32 20.0,5esdsds2sd15870b15aef8dc,30,CharliesAngel (CA),2900.0,1900.0 1560.0,c15e89f2149bcc0cbd5fb204,24,HUH_Token (HUH),400.0,11.75