在 data.frame 的两列之间添加（插入）一列

Question

我有一个包含 a、b 和 c 列的数据框。我想在 b 和 c 之间添加一个新的 d 列。

我知道我可以使用 cbind 在末尾添加 d，但是如何在两列之间插入它？

Answer 1

我会简单地使用cbind()：

> df <- data.frame(a=1:5,
+                  b=10:14,
+                  c=rep(0,5),
+                  d=7:11)
> 
> z <- LETTERS[1:5]
> df <- cbind(df[,1:2], z, df[,3:4]) # Puts the z column between 2nd and 3rd column of df
> df
  a  b z c  d
1 1 10 A 0  7
2 2 11 B 0  8
3 3 12 C 0  9
4 4 13 D 0 10
5 5 14 E 0 11

Answer 2

如果您不能假设列 b 出现在 c 之前，您可以使用 match 查找两者的列号，min 获取较低的列号，seq_len 获取序列，直到本栏目。然后您可以先将此索引用作 positive 子集，然后放置新列 d，然后再次将该序列用作 negative 子集。

i <- seq_len(min(match(c("b", "c"), colnames(x))))
data.frame(x[i], d, x[-i])
#cbind(x[i], d, x[-i]) #Alternative
#  a b  d c
#1 1 4 10 7
#2 2 5 11 8
#3 3 6 12 9

如果您知道b 列在c 之前，您可以将新列d 放在b 之后：

i <- seq_len(match("b", colnames(x)))
data.frame(x[i], d, x[-i])
#  a b  d c
#1 1 4 10 7
#2 2 5 11 8
#3 3 6 12 9

数据：

x <- data.frame(a = 1:3, b = 4:6, c = 7:9)
d <- 10:12

Answer 3

df <- data.frame(a=c(1,2), b=c(3,4), c=c(5,6))
df %>%
  mutate(d= a/2) %>%
  select(a, b, d, c)

结果

  a b   d c
1 1 3 0.5 5
2 2 4 1.0 6

我建议在dplyr::mutate 之后使用dplyr::select。它有许多帮助器来选择/取消选择列的子集。

在此问题的上下文中，您选择的顺序将反映在输出 data.frame 中。

Answer 4

您可以使用append() 函数将项目插入向量或列表（数据框是列表）。简单地说：

df <- data.frame(a=c(1,2), b=c(3,4), c=c(5,6))

df <- as.data.frame(append(df, list(d=df$b+df$c), after=2))

或者，如果您想通过名称指定位置，请使用which：

df <- as.data.frame(append(df, list(d=df$b+df$c), after=which(names(df)=="b")))

Answer 5

添加到您的新列中：

df$d <- list/data

然后你可以重新排序。

df <- df[, c("a", "b", "d", "c")]

Answer 6

简单的解决方案。在具有 5 列的数据框中，如果要在 3 到 4 之间插入另一列...

tmp <- data[, 1:3]
tmp$example <- NA # or any value.
data <- cbind(tmp, data[, 4:5]

Answer 7

你可以像下面那样做 -

df <- data.frame(a=1:4, b=5:8, c=9:12)
df['d'] <- seq(10,13)
df <- df[,c('a','b','d','c')]

Answer 8

这是一个如何将列从最后一个位置移动到第一个位置的示例。它结合了[ 和ncol。我认为在这里为忙碌的读者提供一个非常简短的答案会很有用：

d = mtcars
d[, c(ncol(d), 1:(ncol(d)-1))] 

Answer 9

我建议你使用 tibble 包中的函数 add_column()。

library(tibble)
dataset <- data.frame(a = 1:5, b = 2:6, c=3:7)
add_column(dataset, d = 4:8, .after = 2)

请注意，您可以使用列名代替列索引：

add_column(dataset, d = 4:8, .after = "b")

如果更方便的话，或者使用参数.before 而不是.after。

add_column(dataset, d = 4:8, .before = "c")

Answer 10

创建一个示例 data.frame 并向其中添加一列。

df = data.frame(a = seq(1, 3), b = seq(4,6), c = seq(7,9))
df['d'] <- seq(10,12)
df

  a b c  d
1 1 4 7 10
2 2 5 8 11
3 3 6 9 12

按列索引重新排列

df[, colnames(df)[c(1:2,4,3)]]

或按列名

df[, c('a', 'b', 'd', 'c')]

结果是

  a b  d c
1 1 4 10 7
2 2 5 11 8
3 3 6 12 9

Answer 11

R 没有指定添加新列的位置的功能。例如，mtcars$mycol<-'foo'。它总是作为最后一列添加。使用其他方式（例如，dplyr's select()）您可以将 mycol 移动到所需位置。这并不理想，R 可能希望在未来尝试改变它。

Answer 12

假设c 总是紧跟在b 之后，无论b 在您的data.frame 中的哪个位置，此代码都会在b 之后添加一列。

> test <- data.frame(a=1,b=1,c=1)
> test
  a b c
1 1 1 1

> bspot <- which(names(test)=="b")

> data.frame(test[1:bspot],d=2,test[(bspot+1):ncol(test)])
  a b d c
1 1 1 2 1

或者可能更自然：

data.frame(append(test, list(d=2), after=match("b", names(test))))

Answer 13

此函数在数据框中的所有预先存在的列之间插入一个零列。

insertaCols<-function(dad){   
  nueva<-as.data.frame(matrix(rep(0,nrow(daf)*ncol(daf)*2 ),ncol=ncol(daf)*2))  
   for(k in 1:ncol(daf)){   
      nueva[,(k*2)-1]=daf[,k]   
      colnames(nueva)[(k*2)-1]=colnames(daf)[k]  
      }  
   return(nueva)   
  }

Answer 14

为了它的价值，我写了一个函数来做到这一点：

[已删除]

---

我现在用before 和after 功能更新了这个函数，并将place 默认为1。它还具有数据表兼容性：

#####
# FUNCTION: InsertDFCol(colName, colData, data, place = 1, before, after)
# DESCRIPTION: Takes in a data, a vector of data, a name for that vector and a place to insert this vector into
# the data frame as a new column. If you put place = 3, the new column will be in the 3rd position and push the current
# 3rd column up one (and each subsuquent column up one). All arguments must be set. Adding a before and after
# argument that will allow the user to say where to add the new column, before or after a particular column.
# Please note that if before or after is input, it WILL override the place argument if place is given as well. Also, place
# defaults to adding the new column to the front.
#####

InsertDFCol <- function(colName, colData, data, place = 1, before, after) {

  # A check on the place argument.
  if (length(names(data)) < place) stop("The place argument exceeds the number of columns in the data for the InsertDFCol function. Please check your place number")
  if (place <= 0 & (!missing(before) | !(missing(after)))) stop("You cannot put a column into the 0th or less than 0th position. Check your place argument.")
  if (place %% 1 != 0 & (!missing(before) | !(missing(after)))) stop("Your place value was not an integer.")
  if (!(missing(before)) & !missing(after)) stop("You cannot designate a before AND an after argument in the same function call. Please use only one or the other.")

  # Data Table compatability.
  dClass <- class(data)
  data <- as.data.frame(data)

  # Creating booleans to define whether before or after is given.
  useBefore <- !missing(before)
  useAfter <- !missing(after)

  # If either of these are true, then we are using the before or after argument, run the following code.
  if (useBefore | useAfter) {

    # Checking the before/after argument if given. Also adding regular expressions.
    if (useBefore) { CheckChoice(before, names(data)) ; before <- paste0("^", before, "$") }
    if (useAfter) { CheckChoice(after, names(data)) ; after <- paste0("^", after, "$") }

    # If before or after is given, replace "place" with the appropriate number.
    if (useBefore) { newPlace <- grep(before, names(data)) ; if (length(newPlace) > 1) { stop("Your before argument matched with more than one column name. Do you have duplicate column names?!") }}
    if (useAfter) { newPlace <- grep(after, names(data)) ; if (length(newPlace) > 1) { stop("Your after argument matched with more than one column name. Do you have duplicate column names?!") }}
    if (useBefore) place <- newPlace # Overriding place.
    if (useAfter) place <- newPlace + 1 # Overriding place.

  }

  # Making the new column.
  data[, colName] <- colData

  # Finding out how to reorder this.
  # The if statement handles the case where place = 1.
  currentPlace <- length(names(data)) # Getting the place of our data (which should have been just added at the end).
  if (place == 1) {

    colOrder <- c(currentPlace, 1:(currentPlace - 1))

  } else if (place == currentPlace) { # If the place to add the new data was just at the end of the data. Which is stupid...but we'll add support anyway.

    colOrder <- 1:currentPlace

  } else { # Every other case.

    firstHalf <- 1:(place - 1) # Finding the first half on columns that come before the insertion.
    secondHalf <- place:(currentPlace - 1) # Getting the second half, which comes after the insertion.
    colOrder <- c(firstHalf, currentPlace, secondHalf) # Putting that order together.

  }

  # Reordering the data.
  data <- subset(data, select = colOrder)

  # Data Table compatability.
  if (dClass[1] == "data.table") data <- as.data.table(data)

  # Returning.
  return(data)

}

---

我意识到我也没有包括 CheckChoice：

#####
# FUNCTION: CheckChoice(names, dataNames, firstWord == "Oops" message = TRUE)                                                                                               
# DESCRIPTION: Takes the column names of a data frame and checks to make sure whatever "choice" you made (be it 
# your choice of dummies or your choice of chops) is actually in the data frame columns. Makes troubleshooting easier. 
# This function is also important in prechecking names to make sure the formula ends up being right. Use it after 
# adding in new data to check the "choose" options. Set firstWord to the first word you want said before an exclamation point.
# The warn argument (previously message) can be set to TRUE if you only want to 
#####

CheckChoice <- function(names, dataNames, firstWord = "Oops", warn = FALSE) {

  for (name in names) {

    if (warn == TRUE) { if(!(name %in% dataNames)) { warning(paste0(firstWord, "! The column/value/argument, ", name, ", was not valid OR not in your data! Check your input! This is a warning message of that!")) } }
    if (warn == FALSE) { if(!(name %in% dataNames)) { stop(paste0(firstWord, "! The column/value/argument, " , name, ", was not valid OR not in your data! Check your input!")) } }

  }
}

Answer 15

这是一种在数据框的特定位置插入列的快速而肮脏的方法。就我而言，我在原始数据框中有 5 列：c1, c2, c3, c4, c5，我将在 c2 和 c3 之间插入一个新列 c2b。

1) 我们先创建测试数据框：

> dataset <- data.frame(c1 = 1:5, c2 = 2:6, c3=3:7, c4=4:8, c5=5:9)
> dataset
  c1 c2 c3 c4 c5
1  1  2  3  4  5
2  2  3  4  5  6
3  3  4  5  6  7
4  4  5  6  7  8
5  5  6  7  8  9

2) 在我们的数据框末尾添加新列c2b：

> dataset$c2b <- 10:14
> dataset
  c1 c2 c3 c4 c5 c2b
1  1  2  3  4  5  10
2  2  3  4  5  6  11
3  3  4  5  6  7  12
4  4  5  6  7  8  13
5  5  6  7  8  9  14

3) 根据列索引对数据框重新排序。在我的例子中，我想在现有的第 2 列和第 3 列之间插入新的列 (6)。我通过使用向量 c(1:2, 6, 3:5)（相当于 c(1, 2, 6, 3, 4, 5)）来寻址我的数据框中的列来做到这一点。

> dataset <- dataset[,c(1:2, 6, 3:5)]
> dataset
  c1 c2 c2b c3 c4 c5
1  1  2  10  3  4  5
2  2  3  11  4  5  6
3  3  4  12  5  6  7
4  4  5  13  6  7  8
5  5  6  14  7  8  9

那里！

Answer 16

`

data1 <- data.frame(col1=1:4, col2=5:8, col3=9:12)
row.names(data1) <- c("row1","row2","row3","row4")
data1
data2 <- data.frame(col1=21:24, col2=25:28, col3=29:32)
row.names(data2) <- c("row1","row2","row3","row4")
data2
insertPosition = 2
leftBlock <- unlist(data1[,1:(insertPosition-1)])
insertBlock <- unlist(data2[,1:length(data2[1,])])
rightBlock <- unlist(data1[,insertPosition:length(data1[1,])])
newData <- matrix(c(leftBlock, insertBlock, rightBlock), nrow=length(data1[,1]), byrow=FALSE)
newData

`

Answer 17

您想将 z 列添加到旧数据框 (old.df) 由 x 和 y 列定义。

z = rbinom(1000, 5, 0.25)
old.df <- data.frame(x = c(1:1000), y = rnorm(1:1000))
head(old.df)

定义一个名为 new.df 的新数据框

new.df <- data.frame(x = old.df[,1], z, y = old.df[,2])
head(new.df)

Answer 18

您可以使用 [ 重新排序列，或按您想要的顺序显示列。

d <- data.frame(a=1:4, b=5:8, c=9:12)
target <- which(names(d) == 'b')[1]
cbind(d[,1:target,drop=F], data.frame(d=12:15), d[,(target+1):length(d),drop=F])

  a b  d  c
1 1 5 12  9
2 2 6 13 10
3 3 7 14 11
4 4 8 15 12