Adding rows to CSV sorted by ID in Python without reading whole file into memory
I have a CSV file where the first column is an ID like so:
5,a
4,b
2,c
1,d
The rows must always be sorted from the biggest to smallest ID. I have a list of rows that I want to add, without reading the whole original CSV in memory, so I can't just append the rows and sort after. Here is the code I came up with:
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
for new_row in rows_to_add:
for source_row in reader:
if new_row[0] >= int(source_row[0]):
writer.writerow(new_row)
writer.writerow(source_row)
break
writer.writerow(source_row)
else:
# If source reader already reached end of file
writer.writerow(new_row)
for remaining_line in in_file:
out_file.write(remaining_line)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
Result:
7,NEW1
5,a
6,NEW2
4,b
3,NEW3
2,c
1,d
-2,NEW4
This doesn't work correctly if there are two consecutive IDs, 6,NEW2
should be just after 7,NEW1
and I can't figure out the right way to do it.
python csv
add a comment |
I have a CSV file where the first column is an ID like so:
5,a
4,b
2,c
1,d
The rows must always be sorted from the biggest to smallest ID. I have a list of rows that I want to add, without reading the whole original CSV in memory, so I can't just append the rows and sort after. Here is the code I came up with:
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
for new_row in rows_to_add:
for source_row in reader:
if new_row[0] >= int(source_row[0]):
writer.writerow(new_row)
writer.writerow(source_row)
break
writer.writerow(source_row)
else:
# If source reader already reached end of file
writer.writerow(new_row)
for remaining_line in in_file:
out_file.write(remaining_line)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
Result:
7,NEW1
5,a
6,NEW2
4,b
3,NEW3
2,c
1,d
-2,NEW4
This doesn't work correctly if there are two consecutive IDs, 6,NEW2
should be just after 7,NEW1
and I can't figure out the right way to do it.
python csv
add a comment |
I have a CSV file where the first column is an ID like so:
5,a
4,b
2,c
1,d
The rows must always be sorted from the biggest to smallest ID. I have a list of rows that I want to add, without reading the whole original CSV in memory, so I can't just append the rows and sort after. Here is the code I came up with:
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
for new_row in rows_to_add:
for source_row in reader:
if new_row[0] >= int(source_row[0]):
writer.writerow(new_row)
writer.writerow(source_row)
break
writer.writerow(source_row)
else:
# If source reader already reached end of file
writer.writerow(new_row)
for remaining_line in in_file:
out_file.write(remaining_line)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
Result:
7,NEW1
5,a
6,NEW2
4,b
3,NEW3
2,c
1,d
-2,NEW4
This doesn't work correctly if there are two consecutive IDs, 6,NEW2
should be just after 7,NEW1
and I can't figure out the right way to do it.
python csv
I have a CSV file where the first column is an ID like so:
5,a
4,b
2,c
1,d
The rows must always be sorted from the biggest to smallest ID. I have a list of rows that I want to add, without reading the whole original CSV in memory, so I can't just append the rows and sort after. Here is the code I came up with:
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
for new_row in rows_to_add:
for source_row in reader:
if new_row[0] >= int(source_row[0]):
writer.writerow(new_row)
writer.writerow(source_row)
break
writer.writerow(source_row)
else:
# If source reader already reached end of file
writer.writerow(new_row)
for remaining_line in in_file:
out_file.write(remaining_line)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
Result:
7,NEW1
5,a
6,NEW2
4,b
3,NEW3
2,c
1,d
-2,NEW4
This doesn't work correctly if there are two consecutive IDs, 6,NEW2
should be just after 7,NEW1
and I can't figure out the right way to do it.
python csv
python csv
edited Nov 15 '18 at 1:22
sena
asked Nov 15 '18 at 0:36
senasena
134
134
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
You have to use a running pointer for at least one of the lists. In this case, as you can't read the entire CSV, the running pointer can be used for the other list
Following code should work
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
idx = 0
# For each line in file
for source_row in reader:
# Print all rows from rows_to_add that are larger
while rows_to_add[idx][0] > int(source_row[0]):
writer.writerow(rows_to_add[idx])
idx += 1
# Before printing current line from file
writer.writerow(source_row)
# Print remaining rows in rows_to_add
for row in rows_to_add[idx:]:
writer.writerow(row)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
sample output for your in.csv
7,NEW1
6,NEW2
6,NEW2
5,a
4,b
3,NEW3
2,c
1,d
-2,NEW4
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
You have to use a running pointer for at least one of the lists. In this case, as you can't read the entire CSV, the running pointer can be used for the other list
Following code should work
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
idx = 0
# For each line in file
for source_row in reader:
# Print all rows from rows_to_add that are larger
while rows_to_add[idx][0] > int(source_row[0]):
writer.writerow(rows_to_add[idx])
idx += 1
# Before printing current line from file
writer.writerow(source_row)
# Print remaining rows in rows_to_add
for row in rows_to_add[idx:]:
writer.writerow(row)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
sample output for your in.csv
7,NEW1
6,NEW2
6,NEW2
5,a
4,b
3,NEW3
2,c
1,d
-2,NEW4
add a comment |
You have to use a running pointer for at least one of the lists. In this case, as you can't read the entire CSV, the running pointer can be used for the other list
Following code should work
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
idx = 0
# For each line in file
for source_row in reader:
# Print all rows from rows_to_add that are larger
while rows_to_add[idx][0] > int(source_row[0]):
writer.writerow(rows_to_add[idx])
idx += 1
# Before printing current line from file
writer.writerow(source_row)
# Print remaining rows in rows_to_add
for row in rows_to_add[idx:]:
writer.writerow(row)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
sample output for your in.csv
7,NEW1
6,NEW2
6,NEW2
5,a
4,b
3,NEW3
2,c
1,d
-2,NEW4
add a comment |
You have to use a running pointer for at least one of the lists. In this case, as you can't read the entire CSV, the running pointer can be used for the other list
Following code should work
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
idx = 0
# For each line in file
for source_row in reader:
# Print all rows from rows_to_add that are larger
while rows_to_add[idx][0] > int(source_row[0]):
writer.writerow(rows_to_add[idx])
idx += 1
# Before printing current line from file
writer.writerow(source_row)
# Print remaining rows in rows_to_add
for row in rows_to_add[idx:]:
writer.writerow(row)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
sample output for your in.csv
7,NEW1
6,NEW2
6,NEW2
5,a
4,b
3,NEW3
2,c
1,d
-2,NEW4
You have to use a running pointer for at least one of the lists. In this case, as you can't read the entire CSV, the running pointer can be used for the other list
Following code should work
import csv
def main():
rows_to_add = [[7, "NEW1"], [6, "NEW2"], [6, "NEW2"], [3, "NEW3"], [-2, "NEW4"]]
with open("in.csv", "r") as in_file, open("out.csv", "w") as out_file:
reader = csv.reader(in_file)
writer = csv.writer(out_file)
idx = 0
# For each line in file
for source_row in reader:
# Print all rows from rows_to_add that are larger
while rows_to_add[idx][0] > int(source_row[0]):
writer.writerow(rows_to_add[idx])
idx += 1
# Before printing current line from file
writer.writerow(source_row)
# Print remaining rows in rows_to_add
for row in rows_to_add[idx:]:
writer.writerow(row)
with open("out.csv", "r") as out_file:
print(out_file.read())
if __name__ == "__main__":
main()
sample output for your in.csv
7,NEW1
6,NEW2
6,NEW2
5,a
4,b
3,NEW3
2,c
1,d
-2,NEW4
answered Nov 15 '18 at 1:58
KrishnaKrishna
6021515
6021515
add a comment |
add a comment |
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