r中的matrix()和as.matrix()有什么区别？

Question

我跑R中的以下内容并收到了同样的输出都matrix()和as.matrix()现在我不知道它们之间的区别是什么:

> a=c(1,2,3,4)
> a
[1] 1 2 3 4
> matrix(a)
     [,1]
[1,]    1
[2,]    2
[3,]    3
[4,]    4
> as.matrix(a)
     [,1]
[1,]    1
[2,]    2
[3,]    3
[4,]    4

Answer 1

matrix采取data进一步的论点nrow和ncol.

?matrix
 If one of ‘nrow’ or ‘ncol’ is not given, an attempt is made to
 infer it from the length of ‘data’ and the other parameter.  If
 neither is given, a one-column matrix is returned.

as.matrix 是一种针对不同类型具有不同行为的方法,但主要是从n*m输入返回n*m矩阵.

?as.matrix
 ‘as.matrix’ is a generic function.  The method for data frames
 will return a character matrix if there is only atomic columns and
 any non-(numeric/logical/complex) column, applying ‘as.vector’ to
 factors and ‘format’ to other non-character columns.  Otherwise,
 the usual coercion hierarchy (logical < integer < double <
 complex) will be used, e.g., all-logical data frames will be
 coerced to a logical matrix, mixed logical-integer will give a
 integer matrix, etc.

它们之间的区别主要来自输入matrix的形状,as.matrix不关心形状,是否会保持它(尽管细节取决于输入的实际方法,在您的情况下,无量纲向量对应于单个列矩阵.)输入是原始的,逻辑的,整数的,数字的,字符的还是复杂的等等并不重要.

Answer 2

matrix 从第一个参数构造一个矩阵,具有给定数量的行和列.如果提供的对象不足以满足所需的输出,matrix则会回收其元素:例如,matrix(1:2), nrow=3, ncol=4).相反,如果对象太大,那么剩余元素将被丢弃:例如,matrix(1:20, nrow=3, ncol=4).

as.matrix 将其第一个参数转换为矩阵,其尺寸将从输入中推断出来.