如何透视表以使列从R中的可变行值 [英] How to pivot a table to make columns fro a variable row values in R

问题描述

我有一个data.frame，其列为:Month，Store和Demand.

I have a data.frame with the columns: Month, Store and Demand.

Month   Store   Demand
Jan     A   100
Feb     A   150
Mar     A   120
Jan     B   200
Feb     B   230
Mar     B   320

我需要围绕它进行旋转以制作一个新的data.frame或每个月带有列的数组，例如:

I need to pivot it around to make a new data.frame or array with columns for each month, store e.g.:

Store   Jan Feb Mar
A       100 150 120
B       200 230 320

非常感谢您的帮助.我刚开始使用R.

Any help is very much appreciated. I have just started with R.

推荐答案

> df <- read.table(textConnection("Month   Store   Demand
+ Jan     A   100
+ Feb     A   150
+ Mar     A   120
+ Jan     B   200
+ Feb     B   230
+ Mar     B   320"), header=TRUE)

因此，您的月份"列很可能是按字母顺序排列的级别的一个因素 ()

So in all likelihood your Month column is a factor with levels sorted alphabetically ()

> df$Month <- factor(df$Month, levels= month.abb[1:3])
 # Just changing levels was not correct way to handle the problem. 
 # Need to use within a factor(...) call.
> xtabs(Demand ~ Store+Month, df)
      Month
 Store Jan Feb Mar
     A 100 150 120
     B 200 230 320

一种不太明显的方法(因为"I"函数返回其参数):

A slightly less obvious method (since the 'I' function returns its argument):

> with(df, tapply(Demand, list(Store, Month) , I)  )
  Jan Feb Mar
A 100 150 120
B 200 230 320

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