帮助Python中的if else循环

Question

Hi here is my problem. I have a program that calulcates the averages of data in columns. Example

Bob
1
2
3

the output is

Bob
2

Some of the data has 'na's So for Joe

Joe
NA
NA
NA

I want this output to be NA

so I wrote an if else loop

The problem is that it doesn't execute the second part of the loop and just prints out one NA. Any suggestions?

Here is my program:

with open('C://achip.txt', "rtU") as f:
    columns = f.readline().strip().split(" ")
    numRows = 0
    sums = [0] * len(columns)

    numRowsPerColumn = [0] * len(columns) # this figures out the number of columns

    for line in f:
        # Skip empty lines since I was getting that error before
        if not line.strip():
            continue

        values = line.split(" ")
        for i in xrange(len(values)):
            try: # this is the whole strings to math numbers things
                sums[i] += float(values[i])
                numRowsPerColumn[i] += 1
            except ValueError:
                continue 

    with open('c://chipdone.txt', 'w') as ouf:
        for i in xrange(len(columns)):
           if numRowsPerColumn[i] ==0 :
               print 'NA' 
           else:
               print>>ouf, columns[i], sums[i] / numRowsPerColumn[i] # this is the average calculator

The file looks like so:

Joe Bob Sam
1 2 NA
2 4 NA
3 NA NA
1 1  NA

and final output is the names and the averages

Joe Bob Sam 
1.5 1.5 NA

Ok I tried Roger's suggestion and now I have this error:

Traceback (most recent call last): File "C:/avy14.py", line 5, in for line in f: ValueError: I/O operation on closed file

Here is this new code:

with open('C://achip.txt', "rtU") as f: columns = f.readline().strip().split(" ") sums = [0] * len(columns) rows = 0 for line in f: line = line.strip() if not line: continue

rows += 1 for col, v in enumerate(line.split()): if sums[col] is not None: if v == "NA": sums[col] = None else: sums[col] += int(v)

with open("c:/chipdone.txt", "w") as out: for name, sum in zip(columns, sums): print >>out, name, if sum is None: print >>out, "NA" else: print >>out, sum / rows

Answer 1

with open("c:/achip.txt", "rU") as f:
  columns = f.readline().strip().split()
  sums = [0.0] * len(columns)
  row_counts = [0] * len(columns)

  for line in f:
    line = line.strip()
    if not line:
      continue

    for col, v in enumerate(line.split()):
      if v != "NA":
        sums[col] += int(v)
        row_counts[col] += 1

with open("c:/chipdone.txt", "w") as out:
  for name, sum, rows in zip(columns, sums, row_counts):
    print >>out, name,
    if rows == 0:
      print >>out, "NA"
    else:
      print >>out, sum / rows

I'd also use the no-parameter version of split when getting the column names (it allows you to have multiple space separators).

Regarding your edit to include input/output sample, I kept your original format and my output would be:

Joe 1.75
Bob 2.33333333333
Sam NA

This format is 3 rows of (ColumnName, Avg) columns, but you can change the output if you want, of course. :)

Answer 2

Using numpy:

import numpy as np

with open('achip.txt') as f:
    names=f.readline().split()
    arr=np.genfromtxt(f)

print(arr)
# [[  1.   2.  NaN]
#  [  2.   4.  NaN]
#  [  3.  NaN  NaN]
#  [  1.   1.  NaN]]

print(names)
# ['Joe', 'Bob', 'Sam']

print(np.ma.mean(np.ma.masked_invalid(arr),axis=0))
# [1.75 2.33333333333 --]

Answer 3

Using your original code, I would add one loop and edit the print statement

    with open(r'C:\achip.txt', "rtU") as f:
    columns = f.readline().strip().split(" ")
    numRows = 0
    sums = [0] * len(columns)

    numRowsPerColumn = [0] * len(columns) # this figures out the number of columns

    for line in f:
        # Skip empty lines since I was getting that error before
        if not line.strip():
            continue

        values = line.split(" ")

        ### This removes any '' elements caused by having two spaces like
        ### in the last line of your example chip file above
        for count, v in enumerate(values):      
            if v == '':     
                values.pop(count)
        ### (End of Addition)

        for i in xrange(len(values)):
            try: # this is the whole strings to math numbers things
                sums[i] += float(values[i])
                numRowsPerColumn[i] += 1
            except ValueError:
                continue 

    with open('c://chipdone.txt', 'w') as ouf:
        for i in xrange(len(columns)):
           if numRowsPerColumn[i] ==0 :
               print>>ouf, columns[i], 'NA' #Just add the extra parts
           else:
               print>>ouf, columns[i], sums[i] / numRowsPerColumn[i]

This solution also gives the same result in Roger's format, not your intended format.

Answer 4

Solution below is cleaner and has fewer lines of code ...

import pandas as pd

# read the file into a DataFrame using read_csv
df = pd.read_csv('C://achip.txt', sep="\s+")

# compute the average of each column
avg = df.mean()

# save computed average to output file
avg.to_csv("c:/chipdone.txt")

They key to the simplicity of this solution is the way the input text file is read into a Dataframe. Pandas read_csv allows you to use regular expressions for specifying the sep/delimiter argument. In this case, we used the "\\s+" regex pattern to take care of having one or more spaces between columns.

Once the data is in a dataframe, computing the average and saving to a file can all be done with straight forward pandas functions.