使用列索引和循环来转换数据框

2024-05-04 • 问答

我正在尝试编写一个使用索引的功能，该功能接受键值对并将其堆叠。

这是我的数据：

mydata<-structure(list(groupA = c("Rugby for Chipmunks","Rugby for Chipmunks","Chafing Explained"),First = c(5,3.57142857142857,5,4.5),groupB = c("pylons for Priests","Eating Creosote","Eating Creosote"),Second = c(4,4,3.16666666666667,2.1666667),groupC = c("Wow for YOU!","Advanced Cats for Bears","Blue Paint Only","Mockingbirds"),Third = c(5,3,NaN,4),groupD = c("How to Sell Pigeons","How to Sell Pigeons","How to Sell Pigoens","Larger Boulders"),Fourth = c(4.3,4.1,3.4),groupE = c("Making Money with Pears","Making Money with Pears","Why Walnuts?","Responding to Idiots Part II"),Fifth = c(5,4.16666666666667)),row.names = c(NA,-4L),class = c("tbl_df","tbl","data.frame"))

我想使用索引，因为将来的任务将使用具有不同列名和宽度的数据框。我的方法使用一个函数来确定一列是否为奇/偶，然后提取成对的列，直到到达最后一个 odd 编号的列。请注意，该函数必须考虑每次提取时所需的奇偶索引顺序（组名和相应分数）：

odd <- function(x) x%%2 != 0
outfile<-list()

moveit<-function(df){
  for (i in 1:dim(df)[2])    # define number of loops
    if (  i==dim(df)[2]-1  )  {break} # stop at least odd-numbered column
    if ( odd(i)==FALSE) {next}  # skip when i is not an odd numbered index 
  print(i)
  outfile[[i+1]]<-df[,c(i,i+1)]
}

result<-moveit(mydata)
str(result)

您可以看到结果只是最后一个键值对。为什么？如何调整功能以将所有键值对提取到一个数据框中？

1）整形 reshape可以做到这一点，前提是您想要将数据框整形为长形。不使用任何软件包。

nc <- ncol(mydata)
ig <- seq(1,nc,2)  # indexes of key columns
reshape(as.data.frame(mydata),dir = "long",varying = list(ig,-ig),v.names = c("key","value"))

给予：

    time                          key    value id
1.1    1          Rugby for Chipmunks 5.000000  1
2.1    1          Rugby for Chipmunks 3.571429  2
3.1    1          Rugby for Chipmunks 5.000000  3
4.1    1            Chafing Explained 4.500000  4
1.2    2           Pylons for Priests 4.000000  1
2.2    2              Eating Creosote 4.000000  2
3.2    2              Eating Creosote 3.166667  3
4.2    2              Eating Creosote 2.166667  4
1.3    3                 Wow for YOU! 5.000000  1
2.3    3      Advanced Cats for Bears 3.000000  2
3.3    3              Blue Paint Only      NaN  3
4.3    3                 Mockingbirds 4.000000  4
1.4    4          How to Sell Pigeons 4.300000  1
2.4    4          How to Sell Pigeons 3.000000  2
3.4    4          How to Sell Pigoens 4.100000  3
4.4    4              Larger Boulders 3.400000  4
1.5    5      Making Money with Pears 5.000000  1
2.5    5      Making Money with Pears 3.000000  2
3.5    5                 Why Walnuts? 5.000000  3
4.5    5 Responding to Idiots Part II 4.166667  4

2）ivot_longer 这可以通过pivot_longer

来完成

library)(dplyr)
library(tidyr)

v.names <- c("key","value")
mydata %>%
  setNames(outer(v.names,1:(ncol(.)/2),paste)) %>%
  mutate(id = 1:n()) %>%
  pivot_longer(cols = -id,names_to = c(".value","no"),names_sep = " ") %>%
  arrange(no,id)

请注意，这类似于此处使用pivot_longer：Pivot by group for unequal data size

修改后的主题

这是您的代码修改了。

moveit <- function(df) {
  outfile <- list()
  for(i in seq_along(df)) if (odd(i)) outfile[[(i+1)/2]] <- df[c(i,i+1)]
  outfile
}

我们可以使用gl和split数据集创建数字索引到list的{{1}}，data.frame rename元素和{ {1}}并逐行加入

list

以上内容也可以做成map

library(dplyr)
library(purrr)
split.default(mydata,as.integer(gl(ncol(mydata),2,ncol(mydata)))) %>% 
      map_dfr(~ .x %>% 
                  rename_all(~ c('group','value')))

在OP的代码中，'outfile'No package zone的长度为0。相反，它可以为

lst1 <-  split.default(mydata,ncol(mydata)))) 
do.call(rbind,lapply(lst1,setNames,c("group","value")))

另外，主要问题是最后没有返回'outfile'

list

注意：这里也没有使用任何软件包

使用列索引和循环来转换数据框

xuming_11 回答：使用列索引和循环来转换数据框

修改后的主题

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