I know how to avoid this error, but I donot know why this error happen if I run it in this way.
datain <- data.frame(
chrom = c("chr17", "chr4", "chr5", "chr13"),
map = c(81061047, 106061533, 40102442, 73791553),
rs = c("rs75954926", "rs7679673", "rs7708610", "rs78341008"),
start = c(79061048, 104061534, 38102443, 71791554),
end = c(83061048, 108061534, 42102443, 75791554)
)
datain
datain$chr<-datain$chrom
setDT(datain)
setkey(datain, chr, start, end)
datain
Thanks!
Alex
I can reproduce this with data.table 1.12.0 on both Windows 10 and macOS 10.13.6. After upgrading my macOS system tot data.table 1.12.2 I can confirm that all examples below give the same result.
A somewhat simpler example:
> set.seed(1)
> d <- data.frame(x = paste0("chr",sample(17)[3:6]), y = 1:4)
> d$x2 <- d$x
> d
x y x2
1 chr9 1 chr9
2 chr13 2 chr13
3 chr3 3 chr3
4 chr11 4 chr11
> setDT(d)
> setkey(d,x2,y)
> d
x y x2
1: chr9 4 chr9
2: chr13 2 chr13
3: chr3 3 chr3
4: chr11 1 chr11
This happens also when you assign the key directly with setDT
(which could be expected as setDT
uses setkeyv
to set the keys):
> set.seed(1)
> d <- data.frame(x = paste0("chr",sample(17)[3:6]), y = 1:4)
> d$x2 <- d$x
> d
x y x2
1 chr9 1 chr9
2 chr13 2 chr13
3 chr3 3 chr3
4 chr11 4 chr11
> setDT(d, key = c("x2","y"))
> d
x y x2
1: chr9 4 chr9
2: chr13 2 chr13
3: chr3 3 chr3
4: chr11 1 chr11
As you can see the order of the y
-column is changed, while the order of the other columns is not. Apparently this is only happening when you copy a column the data.frame way, then use setDT
and then use setkey
. Consider the following five cases which all give the intended result:
1) not copying a dataframe column
> set.seed(1)
> d <- data.frame(x = paste0("chr",sample(17)[3:6]), y = 1:4)
> d
x y
1 chr9 1
2 chr13 2
3 chr3 3
4 chr11 4
> setDT(d)
> setkey(d,x)
> d
x y
1: chr11 4
2: chr13 2
3: chr3 3
4: chr9 1
2) creating an arbitrary new column in the dataframe
> set.seed(1)
> d <- data.frame(x = paste0("chr",sample(17)[3:6]), y = 1:4)
> set.seed(1)
> d$x2 <- paste0("chr",sample(17)[1:4])
> d
x y x2
1 chr9 1 chr5
2 chr13 2 chr6
3 chr3 3 chr9
4 chr11 4 chr13
> setDT(d)
> setkey(d,x2,y)
> d
x y x2
1: chr11 4 chr13
2: chr9 1 chr5
3: chr13 2 chr6
4: chr3 3 chr9
3) creating a new column by sampling an existing column and pasting some extr charachters to it
> set.seed(1)
> d <- data.frame(x = paste0("chr",sample(17)[3:6]), y = 1:4)
> set.seed(1)
> d$x2 <- paste0("new_",sample(d$x,4))
> d
x y x2
1 chr9 1 new_chr13
2 chr13 2 new_chr11
3 chr3 3 new_chr3
4 chr11 4 new_chr9
> setDT(d)
> setkey(d,x2,y)
> d
x y x2
1: chr13 2 new_chr11
2: chr9 1 new_chr13
3: chr3 3 new_chr3
4: chr11 4 new_chr9
4) creating a new column by just sampling an existing column
> set.seed(1)
> d <- data.frame(x = paste0("chr",sample(17)[3:6]), y = 1:4)
> set.seed(1)
> d$x2 <- sample(d$x,4)
> d
x y x2
1 chr9 1 chr13
2 chr13 2 chr11
3 chr3 3 chr3
4 chr11 4 chr9
> setDT(d)
> setkey(d,x2,y)
> d
x y x2
1: chr13 2 chr11
2: chr9 1 chr13
3: chr3 3 chr3
4: chr11 4 chr9
5) copying a column the data.table way
> set.seed(1)
> d <- data.frame(x = paste0("chr",sample(17)[3:6]), y = 1:4)
> d
x y
1 chr9 1
2 chr13 2
3 chr3 3
4 chr11 4
> setDT(d)
> d[, x2 := x][]
x y x2
1: chr9 1 chr9
2: chr13 2 chr13
3: chr3 3 chr3
4: chr11 4 chr11
> setkey(d,x2,y)
> d
x y x2
1: chr11 4 chr11
2: chr13 2 chr13
3: chr3 3 chr3
4: chr9 1 chr9
Although this bug seems to occur in a (very) specific usecase, this might be critical for me because I use setkey
in several production systems. Will check whether this specific case occurs in my production code.
Confirming @jaapwalhout's observations (with data.table_1.12.3).
Also, (i) thought it might be related to factors but it's not (happens also with character or integer), (ii) it happens whatever the key (x or y).
Below, a simpler reproducible example.
The warning in the assignment may be related but I'm not sure to understand it.
options(datatable.verbose = TRUE)
## KO
d <- data.frame(x = c(9, 1), y = c(9, 1))
d$x2 <- d$x
d
# x y x2
# 1 9 9 9
# 2 1 1 1
setDT(d, key = "x")[]
# forder took 0 sec
# reorder took 0 sec
# x y x2
# 1: 9 1 9
# 2: 1 9 1
## KO
d <- data.frame(x = c("9", "1"), y = c(9, 1), stringsAsFactors = FALSE)
d$x2 <- d$x
d
# x y x2
# 1 9 9 9
# 2 1 1 1
setDT(d, key = "x")[]
# forder took 0 sec
# reorder took 0 sec
# x y x2
# 1: 9 1 9
# 2: 1 9 1
## OK (with warning)
d <- data.frame(x = c("9", "1"), y = c(9, 1))
setDT(d)
d$x2 <- d$x
# Assigning to all 2 rows
# RHS for item 1 has been duplicated because NAMED is 2, but then is being plonked. length(values)==2; length(cols)==1)
setkey(d, y, verbose = TRUE)[]
# forder took 0 sec
# reorder took 0 sec
# x y x2
# 1: 1 1 1
# 2: 9 9 9
iiuc, when duplicating a column or list element without modification, the memory address will be the same and setting the key will "mess things up".
Works ok when using copy()
.
# KO
l <- list(x = c(9, 1), y = c(9, 1))
l[["z"]] <- l[["x"]]
l
setDT(l, key = "x")[]
address(l$x) == address(l$z)
# TRUE
# OK
l <- list(x = c(9, 1), y = c(9, 1))
l[["z"]] <- copy(l[["x"]])
l
setDT(l, key = "x")[]
Most helpful comment
iiuc, when duplicating a column or list element without modification, the memory address will be the same and setting the key will "mess things up".
Works ok when using
copy()
.