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I need to sort a data.table on multiple columns provided as character vector of variable names.
This is my approach so far:
DT = data.table(x = rep(c("b","a","c"), each = 3), y = c(1,3,6), v = 1:9)
#column names to sort by, stored in a vector
keycol <- c("x", "y")
DT[order(keycol)]
x y v
1: b 1 1
2: b 3 2
Somehow It displays just 2 rows and removes other records. But if I do this:
DT[order(x, y)]
x y v
1: a 1 4
2: a 3 5
3: a 6 6
4: b 1 1
5: b 3 2
6: b 6 3
7: c 1 7
8: c 3 8
9: c 6 9
It works like fluid. Can anyone help with sorting using column name vector?
298
Right-click a field name and click Advanced Sorting. Click the Sort by arrow and click the first field by which you want to sort. Click Ascending or Descending to choose the sort order. Click the Then sort by arrow, click the next field, then choose a sort order.
Sort Rows by Multiple Columns using arrange() In R, the arrange() can also be used to sort the dataframe by multiple columns in ascending or descending order, By default it will sort in ascending order. It will take the dataframe name as the first parameter and column names as the next parameter.
Grouping can be also done using multiple columns belonging to the data frame for this just the names of the columns have to be passed to the function.
To sort a data frame in R, use the order( ) function. By default, sorting is ASCENDING. Prepend the sorting variable by a minus sign to indicate DESCENDING order. Here are some examples.
You need ?setorderv and its cols argument:
A character vector of column names of
xby which to order
library(data.table)
DT = data.table(x=rep(c("b","a","c"),each=3), y=c(1,3,6), v=1:9)
#column vector
keycol <-c("x","y")
setorderv(DT, keycol)
DT
x y v
1: a 1 4
2: a 3 5
3: a 6 6
4: b 1 1
5: b 3 2
6: b 6 3
7: c 1 7
8: c 3 8
9: c 6 9
Note that there is no need to assign the output of setorderv back to DT. The function updates DT by reference.
89
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