python - Pandas - 使用数据框值作为字符串填充列表

Question

我正在从文件夹中读取 csv 文件，然后将 tem 过滤到 pandas 数据框中，如下所示:

results=[]
for filename in glob.glob(os.path.join('/path/*.csv')):
  with open(filename) as p:
    df = pd.read_csv(p)

    filtered = df[(df['duration'] > low1) & (df['duration'] < high1)]

    artist = filtered['artist'].values
    print artist
    track = filtered['track'].values
    print track

其中 low1 = 0，high_1 = 0.5

artist 和 track 将数百个过滤后的项目打印为普通字符串，但如果我尝试将它们附加到循环中的 results 中:

artist = filtered['artist'].values
track = filtered['track'].values
results.append([track,artist]) 

我发现我正在追加对象和类型，results 最终填充了一部分筛选项。我不明白会发生什么。

如何以这种方式将所有项目作为常规 strings 填充 results:

[['artist1', 'track1'], ['artist1', 'track2], ...]]

Answer 1

创建 DataFrame 列表，然后通过 concat 将它们连接在一起, 最后转换为嵌套列表:

results=[]
for filename in glob.glob(os.path.join('/path/*.csv')):
    df = pd.read_csv(filename)
    #filter by conditions and also columns by names with .loc
    filtered = df.loc[(df['duration'] > low1) & (df['duration'] < high1), ['artist','track']]
    #alternative solution 
    filtered = df.loc[df['duration'].between(low1, high1,inclusive=False), ['artist','track']]
    results.append(filtered) 

out = pd.concat(results).values.tolist()

另一个解决方案是附加列表，最后通过列表推导将它们展平:

results=[]
for filename in glob.glob(os.path.join('/path/*.csv')):
    df = pd.read_csv(filename)
    #filter by conditions and also columns by names with .loc
    mask = df['duration'].between(low1, high1,inclusive=False)
    filtered = df.loc[mask, ['artist','track']].values.tolist()
    results.append(filtered) 

out = [y for x in results for y in x]