R中指定列数的矩阵的rowsum

Question

我试图得到R中某一行的矩阵中列的总和。但是，我不希望将整个行相加，而是只需要指定数量的列，即在本例中，对角线上的所有列。我尝试过sum和rowSums函数，但它们要么给我带来奇怪的结果，要么给我一条错误消息。为了进行说明，请参见下面的8x8矩阵的示例代码。对于第一行，我需要除1,1项之外的行的总和，对于第二行，我需要除2,1和2,2等项之外的总和。

m1 <- matrix(c(0.2834803,0.6398198,0.0766999,0.0000000,0.0000000,0.0000000,0.0000000,0.0000000,
               0.0000000,0.1101746,0.6354086,0.2544168,0.0000000,0.0000000,0.0000000,0.0000000,
               0.0000000,0.0000000,0.0548145,0.9451855,0.0000000,0.0000000,0.0000000,0.0000000,
               0.0000000,0.0000000,0.0000000,0.3614786,0.6385214,0.0000000,0.0000000,0.0000000,
               0.0000000,0.0000000,0.0000000,0.0000000,0.5594658,0.4405342,0.0000000,0.0000000,
               0.0000000,0.0000000,0.0000000,0.0000000,0.0000000,0.7490395,0.2509605,0.0000000,
               0.0000000,0.0000000,0.0000000,0.0000000,0.0000000,0.0000000,0.5834363,0.4165637,
          0.0000000,0.0000000,0.0000000,0.0000000,0.0000000,0.0000000,0.0000000,1.0000000),
             8, 8, byrow = TRUE, 
             dimnames = list(c("iAAA", "iAA", "iA", "iBBB", "iBB", "iB", "iCCC", "iD"),
                  c("iAAA_p", "iAA_p", "iA_p", "iBBB_p", "iBB_p", "iB_p", "iCCC_p", "iD_p")))

我尝试过以下几种方法：

rowSums(m1[1, 2:8]) --> Error in rowSums(m1[1, 2:8]) : 
  'x' must be an array of at least two dimensions

或者：

sum(m1[1,2]:m1[1,8]) --> wrong result of 0.6398198 (which is item [1,2])

据我所知，rowSums需要一个数组而不是一个向量(尽管不确定为什么)。但我不明白为什么使用sum的第二种方法不起作用。理想情况下，有一些方法可以仅对位于对角线上方的行中的所有列求和。

非常感谢!

Answer 1

问题是您没有将数组传递给rowSums

class(m1[1,2:8])
# [1] "numeric"

这是一个数值向量。使用多个行，它将工作得很好：

class(m1[1:2,2:8])
# [1] "matrix"

rowSums(m1[1:2,2:8])
#     iAAA       iAA 
#0.7165197 1.0000000 

如果要对对角线上方的所有列求和，则可以使用lower.tri将对角线以下的所有元素设置为0 (或者可能是NA)，然后使用rowSums。如果你不想包含对角线元素本身，你可以设置diag = TRUE (感谢@Fabio指出了这一点)：

m1[lower.tri(m1 , diag = TRUE)] <- 0
rowSums(m1)
#     iAAA       iAA        iA      iBBB       iBB        iB      iCCC        iD 
#0.7165197 0.8898254 0.9451855 0.6385214 0.4405342 0.2509605 0.4165637 0.0000000 

#  With 'NA'
m1[lower.tri(m1)] <- NA
rowSums(m1,na.rm=T)
#     iAAA       iAA        iA      iBBB       iBB        iB      iCCC        iD 
#0.7165197 0.8898254 0.9451855 0.6385214 0.4405342 0.2509605 0.4165637 0.0000000