data.table中的行操作

问题描述

我想使用尝试执行简单的总和和平均值，但我得到意想不到的结果。我遵循 for data.table。我发现一种方式工作，但我不知道为什么这个方法在FAQ的第2节不是。
这个方法给我不正确的结果（例如，它给我第一列的值）：

 基因TCGA_04_1348 TCGA_04_1362 genesum 
 1：A1BG 0.94565 0.70585 0.94565 
 2：A1BG-AS 0.97610 1.15850 0.97610 
 3：A1CF 0.00000 0.02105 0.00000 
 4：A2BP1 0.00300 0.04150 0.00300 
 5：A2LD1 4.57975 5.02820 4.57975 
 6：A2M 60.37320 36.09715 60.37320 
  

这给了我想要的结果。

 基因TCGA_04_1348 TCGA_04_1362 genesum 
 1：A1BG 0.94565 0.70585 1.65150 
 2：A1BG-AS 0.97610 1.15850 2.13460 
 3：A1CF 0.00000 0.02105 0.02105 
 4：A2BP1 0.00300 0.04150 0.04450 
 5：A2LD1 4.57975 5.02820 9.60795 
 6：A2M 60.37320 36.09715 96.47035 
  

我有更多的列和行，这只是一个子集。这与我设置键的方式有什么关系吗？

      gene      TCGA_04_1348      TCGA_04_1362   genesum
  1:    A1BG          0.94565          0.70585  0.94565
  2: A1BG-AS          0.97610          1.15850  0.97610
  3:    A1CF          0.00000          0.02105  0.00000
  4:   A2BP1          0.00300          0.04150  0.00300
  5:   A2LD1          4.57975          5.02820  4.57975
  6:     A2M         60.37320         36.09715 60.37320

and this is giving me the desired result

       gene     TCGA_04_1348       TCGA_04_1362 genesum
  1:    A1BG          0.94565          0.70585  1.65150
  2: A1BG-AS          0.97610          1.15850  2.13460
  3:    A1CF          0.00000          0.02105  0.02105
  4:   A2BP1          0.00300          0.04150  0.04450
  5:   A2LD1          4.57975          5.02820  9.60795
  6:     A2M         60.37320         36.09715 96.47035

I have many more columns and rows, this is just a subset. Does this have anything to do with the way I set the key?

 NAME        NROW    MB COLS                                                      KEY
 [1,] dt     20,785  2  gene,TCGA_04_1348_01A,TCGA_04_1362_01A,genesum            gene

解决方案

A few things:

1. dt[, genesum:=lapply(.SD,sum), by=gene] and dt[, genesum:=apply(dt[,-1, with=FALSE],1, sum)] are quite different.

   • dt[, genesum:=lapply(.SD,sum), by=gene] loops over the columns of the .SD data.table and sums them

   • dt[, genesum:=apply(dt[,-1, with=FALSE],1, sum)] is looping over the rows (ie. apply(x, 1, function) applies function to every row in x

2. I think you can get what you want by calling rowSums, like so:

   dt[, genesum := rowSums(dt[, -1, with=FALSE])]
   

Is that what you're after?

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