R：如何使用cast函数在循环中创建矩阵？ [英] R: How to create matrix in a loop using cast-function?

问题描述

我尝试使用 cast 函数在每年列表 code> reshape-package 。当我尝试这一年的一切都很好。查看代码（测试数据集如下！）：

I try to make a yearly country import matrix out of a yearly list using the cast function in the reshape-package. As I try this for a single year everything works fine. See code (test-dataset below!) :

OCTC2011< - cast（OC〜TC，data = Import_Year [[2011] ]，value =Value）

结果是一个矩阵，包含2011年从原始国家

The result is a matrix containing the import-values of the year 2011 from the origin-country (OC) (rows) to the target-country (TC) (columns).

但是，由于我使用由不同年份的不同产品组成的大型数据集，我想要把这个过程放在一个循环中。我尝试了以下操作：

However, as I use a large dataset consisting of different products for different years, I want to put this procedure in a loop. I tried following:

library(reshape)
OCTC <- 0
for(i in 1:length(unique(Import_Year))) 
{
  OCTC[i] <- cast(OC ~ TC, data =Import_Year[[i]], value = "Value")
}

其中传递警告：要替换的项目数不是多个

Which delivers the warning: number of items to replace is not a multiple of replacement length, probably due to a wrong indexing as I'am hardly familiar with loops.

这里我为我的问题生成了一个简单的数据集：

Here I produced a simple dataset for my problem:

OC <- c("A", "A", "B", "B", "C", "C", "D", "D")
TC <- c("Z", "Z", "Y", "Y", "X", "X", "W", "W")
Value <- c(1,2,3,4,5,6,7,8)
Year <- c(2010,2011)
df_import <- data.frame(OC,TC,Value, Year)
Import_Year <- split(df_import, df_import$Year)

我感谢所有的评论。感谢

I appreciate every comment on this. Thanks

推荐答案

如@DavidArenburg评论，您应该使用 dcast 函数使用 value.var 参数从 reshape2 包中。

As @DavidArenburg comments you should probably use the dcast function from the reshape2 package using the value.var argument.

除此之外，循环应该是这样的，以便工作：

Apart from that the loop should be something like this in order to work:

library(reshape2)
OCTC <- list()
for(i in 1:length(unique(Import_Year))) 
{
  OCTC[[length(OCTC)+1]] <- dcast(OC ~ TC, data =Import_Year[[i]], value.var = "Value")
}

$ b b

所以，你使用 list（）（而不是一个值为零的变量）启动一个列表，然后添加每个dcast作为元素到该列表。

So, you initiate a list using list() (and not a variable with the value of zero) and then you add each dcast as an element to that list.

输出：

> OCTC
[[1]]
  OC  W  X  Y  Z
1  A NA NA NA  1
2  B NA NA  3 NA
3  C NA  5 NA NA
4  D  7 NA NA NA

[[2]]
  OC  W  X  Y  Z
1  A NA NA NA  2
2  B NA NA  4 NA
3  C NA  6 NA NA
4  D  8 NA NA NA

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