Sort columns of a dataframe by column name

This is possibly a simple question, but I do not know how to order columns alphabetically.

test = data.frame(C = c(0, 2, 4, 7, 8), A = c(4, 2, 4, 7, 8), B = c(1, 3, 8, 3, 2))

#   C A B
# 1 0 4 1
# 2 2 2 3
# 3 4 4 8
# 4 7 7 3
# 5 8 8 2

I like to order the columns by column names alphab开发者_运维问答etically, to achieve

#   A B C
# 1 4 1 0
# 2 2 3 2
# 3 4 8 4
# 4 7 3 7
# 5 8 2 8

For others I want my own defined order:

#   B A C
# 1 4 1 0
# 2 2 3 2
# 3 4 8 4
# 4 7 3 7
# 5 8 2 8

Please note that my datasets are huge, with 10000 variables. So the process needs to be more automated.

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You can use order on the names, and use that to order the columns when subsetting:

test[ , order(names(test))]
  A B C
1 4 1 0
2 2 3 2
3 4 8 4
4 7 3 7
5 8 2 8

For your own defined order, you will need to define your own mapping of the names to the ordering. This would depend on how you would like to do this, but swapping whatever function would to this with order above should give your desired output.

You may for example have a look at Order a data frame's rows according to a target vector that specifies the desired order, i.e. you can match your data frame names against a target vector containing the desired column order.

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Here's the obligatory dplyr answer in case somebody wants to do this with the pipe.

test %>% 
    select(sort(names(.)))

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test = data.frame(C=c(0,2,4, 7, 8), A=c(4,2,4, 7, 8), B=c(1, 3, 8,3,2))

Using the simple following function replacement can be performed (but only if data frame does not have many columns):

test <- test[, c("A", "B", "C")]

for others:

test <- test[, c("B", "A", "C")]

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An alternative option is to use str_sort() from library stringr, with the argument numeric = TRUE. This will correctly order column that include numbers not just alphabetically:

str_sort(c("V3", "V1", "V10"), numeric = TRUE)

# [1] V1 V3 V10

---

  test[,sort(names(test))]

sort on names of columns can work easily.

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If you only want one or more columns in the front and don't care about the order of the rest:

require(dplyr)
test %>%
  select(B, everything())

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So to have a specific column come first, then the rest alphabetically, I'd propose this solution:

test[, c("myFirstColumn", sort(setdiff(names(test), "myFirstColumn")))]

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Here is what I found out to achieve a similar problem with my data set.

First, do what James mentioned above, i.e.

test[ , order(names(test))]

Second, use the everything() function in dplyr to move specific columns of interest (e.g., "D", "G", "K") at the beginning of the data frame, putting the alphabetically ordered columns after those ones.

select(test, D, G, K, everything())

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Similar to other syntax above but for learning - can you sort by column names?

sort(colnames(test[1:ncol(test)] ))

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another option is..

mtcars %>% dplyr::select(order(names(mtcars)))

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In data.table you can use the function setcolorder:

setcolorder reorders the columns of data.table, by reference, to the new order provided.

Here a reproducible example:

library(data.table)
test = data.table(C = c(0, 2, 4, 7, 8), A = c(4, 2, 4, 7, 8), B = c(1, 3, 8, 3, 2))
setcolorder(test, c(order(names(test))))
test
#>    A B C
#> 1: 4 1 0
#> 2: 2 3 2
#> 3: 4 8 4
#> 4: 7 3 7
#> 5: 8 2 8

^{Created on 2022-07-10 by the reprex package (v2.0.1)}