加载中…R学习日记----expand.grid()函数
(2013-08-09 08:40:46)
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r语言expand.grid()函数数据框r语言经典入门it |
书中的示例是这样的：
========================================
> expand.grid(c=c(5,8),x=c(100,200),sex=c("F","M"))
1 5 100 F
2 8 100 F
3 5 200 F
4 8 200 F
5 5 100 M
6 8 100 M
7 5 200 M
8 8 200 M
========================================
看到这个时候就产生疑问：为什么定义了三个向量，每个向量两个数据，而组合在一起却产生了
共8行的三个字段的数据？
查了资料，没有。看help，没有。
最后想了半天，可能是这个原因。expand.grid()函数产生的数据框中的数据行数的多少是根据初始定义的
各个向量中的数据个数的乘积决定的。按照上面的例子来说就是2*2*2=8共8行数据。
到这里，就找了其他的例子来验证，示例如下：
============================================
> expand.grid(height = seq(60, 80, 5), weight = seq(100, 300,
50),sex = c("Male","Female"))
1 60
100
Male
2 65
100
Male
3 70
100
Male
4 75
100
Male
5 80
100
Male
6 60
150
Male
7 65
150
Male
8 70
150
Male
9 75
150
Male
10 80
150 Male
11 60
200 Male
12 65
200 Male
13 70
200 Male
14 75
200 Male
15 80
200 Male
16 60
250 Male
17 65
250 Male
18 70
250 Male
19 75
250 Male
20 80
250 Male
21 60
300 Male
22 65
300 Male
23 70
300 Male
24 75
300 Male
25 80
300 Male
26 60
100 Female
27 65
100 Female
28 70
100 Female
29 75
100 Female
30 80
100 Female
31 60
150 Female
32 65
150 Female
33 70
150 Female
34 75
150 Female
35 80
150 Female
36 60
200 Female
37 65
200 Female
38 70
200 Female
39 75
200 Female
40 80
200 Female
41 60
250 Female
42 65
250 Female
43 70
250 Female
44 75
250 Female
45 80
250 Female
46 60
300 Female
47 65
300 Female
48 70
300 Female
49 75
300 Female
50 80
300 Female
====================================================================
数据框行数结果=5*5*2=50
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