Question

我这个矩阵名为Sorted。

     [,1]     [,2]       [,3]       [,4]      
[1,] "a"     "14.06863" "11.50424" "333173.1"
[2,] "b"     "14.50265" "11.89501" "387709.7"
[3,] "c"     "14.55234" "11.95746" "402124"  
[4,] "d"     "14.78606" "12.14149" "453059.3"
[5,] "e"     "15.1697"  "12.51004" "496142.1"
[6,] "f"     "14.41104" "11.81296" "539661.3"
[7,] "g"     "14.86976" "12.23968" "603475.4"

我需要的是添加另一列，第5列，它使用前一个列减去第4列的每个值。它会是这样的：

     [,1]     [,2]       [,3]       [,4]        [,5]     
[1,] "a"     "12.06863" "8.50424" "433173.1"   "433173.1 - 0"
[2,] "b"     "12.50265" "8.89501" "487709.7"   "487709.7 - 433173.1 "
[3,] "c"     "12.55234" "8.95746" "502124"     "502124 - 487709.7"
[4,] "d"     "12.78606" "8.14149" "553059.3"   "553059.3 - 502124 "
[5,] "e"     "14.1697"  "8.51004" "596142.1"   "596142.1 - 553059.3"
[6,] "f"     "11.41104" "8.81296" "639661.3"   "639661.3 - 596142.1 "
[7,] "g"     "15.86976" "8.23968" "703475.4"   "703475.4 - 639661.3"

提前致谢。

Answer 1

matrix只能存储一种类型（例如字符，数字）的数据。由于第1列中有字母，因此整个矩阵都被强制转换为字符，因此您无法再对数据执行算术运算。

另一方面，data.frame只要求每个列包含一致类型的数据，而不同的列可以包含不同类型的数据。

从您的矩阵Sorted开始，尝试以下操作：

# Convert the matrix to a data.frame
d <- as.data.frame(Sorted, stringsAsFactors=FALSE)
# Convert all columns except the first to numeric
d[, -1] <- apply(d[, -1], 2, as.numeric)
# Create a new column called diff, which is column 4 minus column 3
d$diff <- d[, 4] - d[, 3]

d

  V1       V2       V3       V4     diff
1  a 14.06863 11.50424 333173.1 333161.6
2  b 14.50265 11.89501 387709.7 387697.8
3  c 14.55234 11.95746 402124.0 402112.0
4  d 14.78606 12.14149 453059.3 453047.2
5  e 15.16970 12.51004 496142.1 496129.6
6  f 14.41104 11.81296 539661.3 539649.5
7  g 14.86976 12.23968 603475.4 603463.2

修改

正如评论中所指出的，diff应该包含第4列中的值与前一行中的值之间的差异。

实现这一目标的一个简单方法是：

d$diff <- c(d[1, 4], diff(d[, 4])) d V1 V2 V3 V4 diff 1 a 14.06863 11.50424 333173.1 333173.1 2 b 14.50265 11.89501 387709.7 54536.6 3 c 14.55234 11.95746 402124.0 14414.3 4 d 14.78606 12.14149 453059.3 50935.3 5 e 15.16970 12.51004 496142.1 43082.8 6 f 14.41104 11.81296 539661.3 43519.2 7 g 14.86976 12.23968 603475.4 63814.1

Answer 2

首先创建样本矩阵

M <- cbind(letters[1:10], matrix(rnorm(30), ncol=3))

使用sapply

在新列中生成值

newcol <- c(M[1,4], 
    sapply(2:10, FUN=function(x) {
        # subtract value at x-1 from value at x
        as.numeric(M[as.numeric(x),4])-as.numeric(M[as.numeric(x)-1,4])} ) )

绑定到原始矩阵

M <- cbind(M, newcol)

Answer 3

如果矩阵名称是M，那么这应该是技巧 - 将创建一个列差异，并从列V4的差异中设置其值。

M $ diff＆lt; - M $ 4
M $ diff [2：长度（M $ V4）]＆lt; - 差异（M $ V4,1）

通过在行之间执行操作将新列添加到矩阵

3 个答案: