读取CSV文件并将数据转换为python列表。 ValueError：无法将字符串转换为float：

Question

I have a CSV file containing adjacency matrix of a network. When I tried to convert this data into python list of lists using the following code:

def main(): 
    csvfile= open('airport_CnToCn_ajc.csv','rU')
    reader = csv.reader(csvfile,delimiter=" ")
    alldata = list(reader)
    print alldata
    numData=[[float(i) for i in row] for row in alldata]
    print numData

I got an error

ValueError: could not convert string to float ,"Afghanistan","Albania","Algeria","American

because first row and first column of my csv file denotes source and destination of the network edges.

Is there an alternate to overcome this error other than modifying the CSV file by deleting first row and first column. If I follow the later approach, I would lose track of the nodes.

Answer 1

If you know the first row and column are not needed, you could skip them in iteration.

def main(): 
    with open('airport_CnToCn_ajc.csv','rU') as csvfile:
      reader = csv.reader(csvfile)
      alldata = list(reader)[1:]
    print alldata
    numData=[[float(i) for i in row[1:]] for row in alldata]
    print numData

Or, to reduce some copies (likely unneeded):

reader_iter = csv.reader(csvfile)
next(reader_iter)
alldata = list(reader_iter)

Answer 2

You have two options here:

1. You can skip the first row and the first column:

    def main(): with open('airport_CnToCn_ajs.csv', 'rU') as csvfile: reader = csv.reader(csvfile, delimiter=',') next(reader) # Skip first row rows = list(reader) data = [float(i) for i in row[1:] for row in rows] # skip first column 

2. You can use a DictReader :

    def main(): with open('airport_CnToCn_ajs.csv', 'rU') as csvfile: reader = csv.DictReader(csvfile, delimiter=',') rows = list(reader) data = [] for row in rows: i = [] i.append(row['columna']) # Your data columns i.append(row['columnb']) data.append(map(float, i)) # convert to float