如何重复减去R中数据矩阵的行 [英] How can repeatedly subtract the rows of a data matrix in R

问题描述

我有一个1000×2的矩阵，如下所示:

I have a 1000×2 matrix as follows:

         A B
Row1     0 2
Row2     0 3
Row3     0 4
Row4     0 5
Row5     0 3
Row6     0 4
         ...
         ...
Row999   0 8
Row1000  0 9

我想向矩阵添加一个新的列C.新列C的元素是通过计算列B的连续块之和的比率获得的.每个块包含两个元素.换句话说，我想得到以下矩阵:

I want to add a new column C to the matrix. The elements of the new column C are obtained by calculating the ratios of the sum of consecutive blocks of Column B. Each block contains two elements. In other words, I want to get the following matrix:

         A B   C
Row1     0 2  2/(2+3)
Row2     0 3  3/(2+3)
Row3     0 4  4/(4+5)
Row4     0 5  5/(4+5)
Row5     0 3  3/(3+4)
Row6     0 4  4/(3+4)
         ...
         ...
Row999   0 8  8/(8+9)
Row1000  0 9  9/(8+9)

我不知道如何在R中执行此操作.有人可以帮助我吗?非常感谢你. (对不起，我的英语表达不好，我不是母语人士.)

I don't know how to do this in R. Could anyone help me with this? Thank you very much. (Sorry for my poor English expression, I am not a native speaker.)

推荐答案

如果m是矩阵，您似乎想对两个元素的连续块求和，就可以做到:

You seem to wanna sum consecutive blocks of two elements, and you can do, if m is your matrix:

library(zoo)

cbind(m, m[,2]/rep(rollapply(m[,2], 2, sum, by=2), each=2))

或基于R:

x = m[,2][!!seq(nrow(m))%% 2] + m[,2][!seq(nrow(m))%% 2]
cbind(m, rep(x, each=2))

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