[英]How to read a CSV file every other row
how do I take from a CSV file data every 2 rows? 如何每2行从CSV文件中获取数据?
For example if I have a file that looks this 例如,如果我有一个看起来像这样的文件
0 1
0 23 34
1 45 45
2 78 16
3 110 78
4 48 14
5 76 23
6 55 33
7 12 13
8 18 76
how can iterate and extract every 2nd row to get something like this and append in a new dataframe? 如何迭代和提取第二行以获得类似的内容并追加到新的数据框中?
0 23 34
2 78 16
4 48 14
6 55 33
8 18 76
Thank you! 谢谢!
Use the skiprows
parameter of read_csv
: 使用
skiprows
的参数read_csv
:
To keep even rows: 要保持偶数行:
pd.read_csv('file.csv', skiprows=lambda x: (x != 0) and not x % 2)
To keep odd rows: 要保留奇数行:
pd.read_csv('file.csv', skiprows=lambda x: x % 2)
Note that the header is included in skiprows
, which is why the x != 0
is needed in the even example. 请注意,标头包含在
skiprows
,这就是为什么在偶数示例中需要x != 0
原因。
Example: 例:
In [1]: import pandas as pd
...: from io import StringIO
...:
...: data = """A,B
...: a,1
...: b,2
...: c,3
...: d,4
...: e,5
...: """
In [2]: pd.read_csv(StringIO(data))
Out[2]:
A B
0 a 1
1 b 2
2 c 3
3 d 4
4 e 5
In [3]: pd.read_csv(StringIO(data), skiprows=lambda x: (x != 0) and not x % 2)
Out[3]:
A B
0 a 1
1 c 3
2 e 5
In [4]: pd.read_csv(StringIO(data), skiprows=lambda x: x % 2)
Out[4]:
A B
0 b 2
1 d 4
you could read them all into memory with numpy
and store every other row: 您可以使用
numpy
将它们全部读取到内存中并存储每隔一行:
import numpy as np
import pandas as pd
data = np.loadtxt(filename)
data = pd.DataFrame(data[::2])
The last bit, [::2]
, means "take every second element". 最后一位
[::2]
表示“每隔第二个元素”。
Personally, I think the easiest answer (if you only want even-numbered rows) is to do: 就我个人而言,我认为最简单的答案是(如果您只想要偶数行):
import pandas as pd
df = pd.read_csv('csv_file.csv')
rows_we_want = [row for i,row in enumerate(df.index) if not i % 2]
df_new = df.loc[rows_we_want]
enumerate() is a powerful function in Python and "if not i % 2" is only True when the row number (i) is even. enumerate()是Python中的强大功能,并且当行号(i)为偶数时,“ if if i%2”仅是True。 You could delete the "not" if you want the odd-numbered rows instead.
如果要改用奇数行,则可以删除“ not”。 I think this approach is easier than reading in the file line-by-line, though there could be scalability issues with this if your file is extremely large.
我认为这种方法比逐行读取文件更容易,尽管如果文件很大,则可能存在可伸缩性问题。 Hope this helps
希望这可以帮助
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