numpy.genfromtxt中的dtype参数 [英] dtype argument in numpy.genfromtxt

问题描述

>>> from io import StringIO
>>> import numpy as np
>>> s = StringIO("1,1.3,abcde")
>>> data = np.genfromtxt(s, dtype=[('myint','i8'),('myfloat','f8'),
... ('mystring','S5')], delimiter=",")
>>> data
array((1, 1.3, 'abcde'),
      dtype=[('myint', '<i8'), ('myfloat', '<f8'), ('mystring', '|S5')])

我的问题与dtype参数有关. 我无法理解dtype="i8,f8,|S5"代表什么. 我可以确定 i 是整数， f 是浮点数，而 s 是字符串，但是i8中的8是什么?我首先以字节为单位理解它，但是s5怎么可能. 我了解 dtype 有助于指定数据类型，以便我们可以从CSV文件读取数据，但是有人可以对数据类型提供一些见识

My question is related to dtype argument. I am unable to understand what dtype="i8,f8,|S5" stands for. I can make out that i is an integer,f is the float and s is the string but what is 8 in i8? I first understood it for bytes but how can then s5 be possible. I understand that dtype helps to specify the data type so that we can read from CSV file but can someone give some insight on data types

推荐答案

i8或f8中的8是字节数.有几种不同的方法可以在numpy中表示相同的数据类型.您从np.genfromtxt中看到的字符串为紧凑格式.前面的<或>符号表示尾数大或小(请参见文档)，后跟i表示整数或f表示浮点/双精度以及字节数.

The 8 in i8 or f8 is the number of bytes. There are several different ways to express the same datatype in numpy. The strings you see from np.genfromtxt are in the compact format. The < or > sign in front mean little or big endian (see documentation), followed by i for integer or f for float/double, and the number of bytes.

较长的数据类型名称的大小为位，而不是字节，这意味着i8是int64，f4是float32，依此类推.例如:

The longer datatype names have the size in bits instead of bytes, meaning that i8 is int64, f4 is float32 and so on. E.g.:

>>> np.dtype('i8')
dtype('int64')
>>> np.dtype('f4')
dtype('float32')

默认情况下，这些都是小尾数法.据我所知，如果要大字节序，np.dtype不会返回长格式:

By default these are all little endian. If you want big endian, as far as I know, np.dtype does not return the long form:

>>> np.dtype('>c16')
dtype('>c16') 

字符串是一种特殊的数据类型，数字表示最大字符串字符数.有关更多详细信息，请参见此问题.

Strings are a special datatype, and the number means the maximum number of string characters. See this question for more details.

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