我如何读取从512 * n到512 *(n + 1)的行?
df = pd.read_csv(fn, header=None, skiprows=512*n, nrows=512)
你可以这样做(而且非常有用):
for chunk in pd.read_csv(f, sep = ' ', header = None, chunksize = 512):
示例:
In [61]: fn = 'd:/temp/a.csv'
In [62]: pd.DataFrame(np.random.randn(30, 3), columns=list('abc')).to_csv(fn, index=False)
In [63]: for chunk in pd.read_csv(fn, chunksize=10):
....: print(chunk)
....:
a b c
0 2.229657 -1.040086 1.295774
1 0.358098 -1.080557 -0.396338
2 0.731741 -0.690453 0.126648
3 -0.009388 -1.549381 0.913128
4 -0.256654 -0.073549 -0.171606
5 0.849934 0.305337 2.360101
6 -1.472184 0.641512 -1.301492
7 -2.302152 0.417787 0.485958
8 0.492314 0.603309 0.890524
9 -0.730400 0.835873 1.313114
a b c
0 1.393865 -1.115267 1.194747
1 3.038719 -0.343875 -1.410834
2 -1.510598 0.664154 -0.996762
3 -0.528211 1.269363 0.506728
4 0.043785 -0.786499 -1.073502
5 1.096647 -1.127002 0.918172
6 -0.792251 -0.652996 -1.000921
7 1.582166 -0.819374 0.247077
8 -1.022418 -0.577469 0.097406
9 -0.274233 -0.244890 -0.352108
a b c
0 -0.317418 0.774854 -0.203939
1 0.205443 0.820302 -2.637387
2 0.332696 -0.655431 -0.089120
3 -0.884916 0.274854 1.074991
4 0.412295 -1.561943 -0.850376
5 -1.933529 -1.346236 -1.789500
6 1.652446 -0.800644 -0.126594
7 0.520916 -0.825257 -0.475727
8 -2.261692 2.827894 -0.439698
9 -0.424714 1.862145 1.103926
"iterator"在哪种情况下会有用?
当使用chunksize
时,所有的块都具有相同的长度。使用iterator
参数,您可以定义每次迭代要读取多少数据 (get_chunk(nrows)
):
In [66]: reader = pd.read_csv(fn, iterator=True)
读取前3行
In [67]: reader.get_chunk(3)
Out[67]:
a b c
0 2.229657 -1.040086 1.295774
1 0.358098 -1.080557 -0.396338
2 0.731741 -0.690453 0.126648
现在我们将读取接下来的5行:
In [68]: reader.get_chunk(5)
Out[68]:
a b c
0 -0.009388 -1.549381 0.913128
1 -0.256654 -0.073549 -0.171606
2 0.849934 0.305337 2.360101
3 -1.472184 0.641512 -1.301492
4 -2.302152 0.417787 0.485958
接下来7行:
In [69]: reader.get_chunk(7)
Out[69]:
a b c
0 0.492314 0.603309 0.890524
1 -0.730400 0.835873 1.313114
2 1.393865 -1.115267 1.194747
3 3.038719 -0.343875 -1.410834
4 -1.510598 0.664154 -0.996762
5 -0.528211 1.269363 0.506728
6 0.043785 -0.786499 -1.073502
chunksize
和iterator
之间的区别... - MaxU - stand with Ukraineiterator = False
和iterator = True
之间的区别。 - Sida Zhoureader = pd.read_csv(input_files[0], header=None, delimiter='!', nrows=10000, dtype='str', chunksize=20, iterator=False)
和print(reader.get_chunk(5)); print(reader.get_chunk(3))
,它可以正常工作。 - Sida Zhou