Trying to use .SD inside by in data.table
I'm trying to use the .SD to groupby inside a data.table to apply a function to a specific column. I'm gonna use iris dataset as an example.
Lets say I want to know how many unique Sepal.Length there is by species.
library(data.table)
obj="Species"
as.data.table(iris)[,length(unique(Sepal.Length)),by=.SD,.SDcols=obj]
It is important that I can supply .SDcols as an object, since I'm doing it programmatically. I also would like to know if it is possible using data.table instead of aggregate and/or xtabs solution.
Appreciate any help.
r data.table
asked Jan 1 at 23:32
Ricardo Fernandes CamposRicardo Fernandes Campos
654415
add a comment |
I'm trying to use the .SD to groupby inside a data.table to apply a function to a specific column. I'm gonna use iris dataset as an example.
Lets say I want to know how many unique Sepal.Length there is by species.
library(data.table)
obj="Species"
as.data.table(iris)[,length(unique(Sepal.Length)),by=.SD,.SDcols=obj]
It is important that I can supply .SDcols as an object, since I'm doing it programmatically. I also would like to know if it is possible using data.table instead of aggregate and/or xtabs solution.
Appreciate any help.
r data.table
asked Jan 1 at 23:32
Ricardo Fernandes CamposRicardo Fernandes Campos
654415
add a comment |
I'm trying to use the .SD to groupby inside a data.table to apply a function to a specific column. I'm gonna use iris dataset as an example.
Lets say I want to know how many unique Sepal.Length there is by species.
library(data.table)
obj="Species"
as.data.table(iris)[,length(unique(Sepal.Length)),by=.SD,.SDcols=obj]
It is important that I can supply .SDcols as an object, since I'm doing it programmatically. I also would like to know if it is possible using data.table instead of aggregate and/or xtabs solution.
Appreciate any help.
r data.table
asked Jan 1 at 23:32
Ricardo Fernandes CamposRicardo Fernandes Campos
654415
I'm trying to use the .SD to groupby inside a data.table to apply a function to a specific column. I'm gonna use iris dataset as an example.
Lets say I want to know how many unique Sepal.Length there is by species.
library(data.table)
obj="Species"
as.data.table(iris)[,length(unique(Sepal.Length)),by=.SD,.SDcols=obj]
It is important that I can supply .SDcols as an object, since I'm doing it programmatically. I also would like to know if it is possible using data.table instead of aggregate and/or xtabs solution.
Appreciate any help.
r data.table
r data.table
asked Jan 1 at 23:32
Ricardo Fernandes CamposRicardo Fernandes Campos
654415
asked Jan 1 at 23:32
Ricardo Fernandes CamposRicardo Fernandes Campos
654415
asked Jan 1 at 23:32
Ricardo Fernandes CamposRicardo Fernandes Campos
654415
asked Jan 1 at 23:32
Ricardo Fernandes CamposRicardo Fernandes Campos
654415
asked Jan 1 at 23:32
Ricardo Fernandes CamposRicardo Fernandes Campos
654415
654415
add a comment |
add a comment |
1 Answer
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We could directly pass the 'obj' in by and get the length of unique elements of 'Sepal.Length' (uniqueN)
as.data.table(iris)[, .(uniqueLen = uniqueN(Sepal.Length)), by = obj]
If we wanted to go by the .SDcols route
as.data.table(iris)[, .SD[, .(uniqueLen = uniqueN(.SD[[1]])), by = obj],
.SDcols = c(obj, "Sepal.Length")]
answered Jan 1 at 23:35
akrunakrun
411k13199274
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1 Answer
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1 Answer
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active
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We could directly pass the 'obj' in by and get the length of unique elements of 'Sepal.Length' (uniqueN)
as.data.table(iris)[, .(uniqueLen = uniqueN(Sepal.Length)), by = obj]
If we wanted to go by the .SDcols route
as.data.table(iris)[, .SD[, .(uniqueLen = uniqueN(.SD[[1]])), by = obj],
.SDcols = c(obj, "Sepal.Length")]
answered Jan 1 at 23:35
akrunakrun
411k13199274
add a comment |
We could directly pass the 'obj' in by and get the length of unique elements of 'Sepal.Length' (uniqueN)
as.data.table(iris)[, .(uniqueLen = uniqueN(Sepal.Length)), by = obj]
If we wanted to go by the .SDcols route
as.data.table(iris)[, .SD[, .(uniqueLen = uniqueN(.SD[[1]])), by = obj],
.SDcols = c(obj, "Sepal.Length")]
answered Jan 1 at 23:35
akrunakrun
411k13199274
add a comment |
We could directly pass the 'obj' in by and get the length of unique elements of 'Sepal.Length' (uniqueN)
as.data.table(iris)[, .(uniqueLen = uniqueN(Sepal.Length)), by = obj]
If we wanted to go by the .SDcols route
as.data.table(iris)[, .SD[, .(uniqueLen = uniqueN(.SD[[1]])), by = obj],
.SDcols = c(obj, "Sepal.Length")]
answered Jan 1 at 23:35
akrunakrun
411k13199274
We could directly pass the 'obj' in by and get the length of unique elements of 'Sepal.Length' (uniqueN)
as.data.table(iris)[, .(uniqueLen = uniqueN(Sepal.Length)), by = obj]
If we wanted to go by the .SDcols route
as.data.table(iris)[, .SD[, .(uniqueLen = uniqueN(.SD[[1]])), by = obj],
.SDcols = c(obj, "Sepal.Length")]
answered Jan 1 at 23:35
akrunakrun
411k13199274
edited Jan 1 at 23:54
answered Jan 1 at 23:35
akrunakrun
411k13199274
answered Jan 1 at 23:35
akrunakrun
411k13199274
answered Jan 1 at 23:35
akrunakrun
411k13199274
411k13199274
add a comment |
add a comment |
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