Question

我有一个数据框：

import pandas as pd
df = pd.DataFrame({'start' : [5, 10, '$%%', 20], 'stop' : [10, 20, 30, 40]})
df['length_of_region'] = pd.Series([0 for i in range(0, len(df['start']))])

我想仅针对非零数字行值计算区域长度，并且如果值不正确则跳过具有错误注释的行的函数。以下是我到目前为止的情况：

df['Notes'] = pd.Series(["" for i in range(0, len(df['region_name']))])

for i in range(0, len(df['start'])):
    if pd.isnull(df['start'][i]) == True:
        df['Notes'][i] += 'Error: Missing value for chromosome start at region %s, required value;' % (df['region_name'][i])
        df['critical_error'][i] = True
        num_error = num_error+1
    else:
        try:
            #print (df['start'][i]).isnumeric()
            start = int(df['start'][i])
            #print start
            #print df['start'][i]
            if start == 0:
                raise ValueError
        except:
            df['Notes'][i] += 'Error: Chromosome start should be a non zero number at region %s; ' % (df['region_name'][i])
            #print df['start'][i]
            df['critical_error'][i] = True
            num_error = num_error+1
for i in range(0, len(df['start'][i])):
    if df['critical_error'][i] == True:
        continue
    df['length_of_region'][i] = (df['stop'][i] - df['start'][i]) + 1.0

但是，pandas会将df['start']转换为str变量，即使我使用int进行转换，也会出现以下错误：

df['length_of_region'][i] = (df['stop'][i] - df['start'][i]) + 1.0

TypeError：不支持的操作数类型 - ：＆＃39; numpy.int64＆＃39;和＆＃39; str＆＃39;

我在这里缺少什么？谢谢你的时间！

Answer 1

您可以定义自定义函数来进行计算，然后将该函数应用于每一行。

def calculate_region_length(x):
    start_val = x[0]
    stop_val = x[1]
    try:
        start_val = float(start_val)
        return (stop_val - start_val) + 1.0
    except ValueError:
        return None

自定义函数接受列表作为输入。该函数将测试起始值以查看它是否可以转换为浮点数。如果不能，则返回None。这种方式如果＆＃39; 1＆＃39;作为字符串存储，该值仍然可以转换为浮点数并且不会被跳过，而＆＃39; $ %%＆＃39;在您的示例中不能并且将返回None。

接下来，为每一行调用自定义函数：

df['length_of_region'] = df[['start', 'stop']].apply(lambda x: calculate_region_legnth(x), axis=1)

这将为(stop - start) + 1.0创建新列，其中start不是不可转换的字符串，None其中start是无法转换为的字符串一个数字。

然后，您可以根据返回Notes的行更新None字段，以确定缺少起始值的区域：

df.loc[df['length_of_region'].isnull(), 'Notes'] = df['region_name']

Answer 2

在盯着代码一段时间之后，找到了一个简单而优雅的解决方法，将df['start'][i]重新分配给start try-except，如下所示：

for i in range(0, len(df['start'])):
    if pd.isnull(df['start'][i]) == True:
        df['Notes'][i] += 'Error: Missing value for chromosome start at region %s, required value;' % (df['region_name'][i])
        df['critical_error'][i] = True
        num_error = num_error+1
    else:
        try:
            start = int(df['start'][i])
            df['start'][i] = start
            if start == 0:
                raise ValueError
        except:
            df['Notes'][i] += 'Error: Chromosome start should be a non zero number at region %s; ' % (df['region_name'][i])
            #print df['start'][i]
            df['critical_error'][i] = True
            num_error = num_error+1
for i in range(0, len(df['start'][i])):
    if df['critical_error'][i] == True:
        continue
    df['length_of_region'][i] = (df['stop'][i] - df['start'][i]) + 1.0

重新分配起始变量，将其转换为int格式并帮助仅为数字列计算length_of_region

如果在pandas dataframe中为非数字，则跳过对行的操作

2 个答案: