How to use laply match to lookup value and append in each row?
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1
down vote
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I have two data tables as below:
library(data.table)
x <- data.table(id = c(1,1,1,2,2,2,3,3,3,4,4,4), date = as.Date(c("2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03")))
y <- data.table(id=c(1,2,3,4),new_id=c(10,20,30,40))
As mentioned now I want to append the new_id column in the data table x and then later drop column id .
I can do this by
merge(x,y,by="id")
But I wanted to try the lapply .
So I tried
x[,new_id:=0]
nm <- c("new_id")
x[nm] <- lapply(nm, function(z) y[[z]][match(y$id, x$id)])
Also which method will be good if I have wide columns and more rows.
It does not matches the column it seems.
Also which method will be efficient if I have wide columns and more rows.
Any help is appreciated.
r dplyr data.table
add a comment |
up vote
1
down vote
favorite
I have two data tables as below:
library(data.table)
x <- data.table(id = c(1,1,1,2,2,2,3,3,3,4,4,4), date = as.Date(c("2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03")))
y <- data.table(id=c(1,2,3,4),new_id=c(10,20,30,40))
As mentioned now I want to append the new_id column in the data table x and then later drop column id .
I can do this by
merge(x,y,by="id")
But I wanted to try the lapply .
So I tried
x[,new_id:=0]
nm <- c("new_id")
x[nm] <- lapply(nm, function(z) y[[z]][match(y$id, x$id)])
Also which method will be good if I have wide columns and more rows.
It does not matches the column it seems.
Also which method will be efficient if I have wide columns and more rows.
Any help is appreciated.
r dplyr data.table
1
If you are usingmatch
, then you don't needlapply
i.e.y$new_id[match(x$id, y$id)]
– akrun
Nov 8 at 5:24
I guess you are just looking for an update join:x[, new_id := y[x, on=.(id), x.id]]
the x.* prefix refers to the x table's columns in j ofx[i,on=, j]
– Frank
Nov 8 at 11:06
add a comment |
up vote
1
down vote
favorite
up vote
1
down vote
favorite
I have two data tables as below:
library(data.table)
x <- data.table(id = c(1,1,1,2,2,2,3,3,3,4,4,4), date = as.Date(c("2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03")))
y <- data.table(id=c(1,2,3,4),new_id=c(10,20,30,40))
As mentioned now I want to append the new_id column in the data table x and then later drop column id .
I can do this by
merge(x,y,by="id")
But I wanted to try the lapply .
So I tried
x[,new_id:=0]
nm <- c("new_id")
x[nm] <- lapply(nm, function(z) y[[z]][match(y$id, x$id)])
Also which method will be good if I have wide columns and more rows.
It does not matches the column it seems.
Also which method will be efficient if I have wide columns and more rows.
Any help is appreciated.
r dplyr data.table
I have two data tables as below:
library(data.table)
x <- data.table(id = c(1,1,1,2,2,2,3,3,3,4,4,4), date = as.Date(c("2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03","2015-5-26","2015-6-15","2015-4-03")))
y <- data.table(id=c(1,2,3,4),new_id=c(10,20,30,40))
As mentioned now I want to append the new_id column in the data table x and then later drop column id .
I can do this by
merge(x,y,by="id")
But I wanted to try the lapply .
So I tried
x[,new_id:=0]
nm <- c("new_id")
x[nm] <- lapply(nm, function(z) y[[z]][match(y$id, x$id)])
Also which method will be good if I have wide columns and more rows.
It does not matches the column it seems.
Also which method will be efficient if I have wide columns and more rows.
Any help is appreciated.
r dplyr data.table
r dplyr data.table
edited Nov 8 at 4:39
asked Nov 8 at 4:36
Ricky
6621323
6621323
1
If you are usingmatch
, then you don't needlapply
i.e.y$new_id[match(x$id, y$id)]
– akrun
Nov 8 at 5:24
I guess you are just looking for an update join:x[, new_id := y[x, on=.(id), x.id]]
the x.* prefix refers to the x table's columns in j ofx[i,on=, j]
– Frank
Nov 8 at 11:06
add a comment |
1
If you are usingmatch
, then you don't needlapply
i.e.y$new_id[match(x$id, y$id)]
– akrun
Nov 8 at 5:24
I guess you are just looking for an update join:x[, new_id := y[x, on=.(id), x.id]]
the x.* prefix refers to the x table's columns in j ofx[i,on=, j]
– Frank
Nov 8 at 11:06
1
1
If you are using
match
, then you don't need lapply
i.e. y$new_id[match(x$id, y$id)]
– akrun
Nov 8 at 5:24
If you are using
match
, then you don't need lapply
i.e. y$new_id[match(x$id, y$id)]
– akrun
Nov 8 at 5:24
I guess you are just looking for an update join:
x[, new_id := y[x, on=.(id), x.id]]
the x.* prefix refers to the x table's columns in j of x[i,on=, j]
– Frank
Nov 8 at 11:06
I guess you are just looking for an update join:
x[, new_id := y[x, on=.(id), x.id]]
the x.* prefix refers to the x table's columns in j of x[i,on=, j]
– Frank
Nov 8 at 11:06
add a comment |
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1
If you are using
match
, then you don't needlapply
i.e.y$new_id[match(x$id, y$id)]
– akrun
Nov 8 at 5:24
I guess you are just looking for an update join:
x[, new_id := y[x, on=.(id), x.id]]
the x.* prefix refers to the x table's columns in j ofx[i,on=, j]
– Frank
Nov 8 at 11:06