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I have a function that returns a data.table with various useful user-defined attributes attached. I notice, though, that the attributes disappear when one manipulates the data.table.
library(data.table)
my_dt <- data.table(col1 = rnorm(20), col2 = letters[1:20])
# store some user attribute
attr(my_dt, 'title') <- 'This is my data.table'
# now it's there
attributes(my_dt)
# but here it's gone
attributes(my_dt[order(col1)])
Is there any way to make attributes of a data.table 'persist' for cases like the above (besides just storing them in a separate object)?
It seems attributes do persist for regular data.frames
my_df <- data.frame(col1 = rnorm(20), col2 = letters[1:20])
# store some user attribute
attr(my_df, 'title') <- 'This is my data.frame'
# there it is
attributes(my_df)
# still there
attributes(my_df[order(my_df$col1), ])
805
It offers fast and memory efficient: file reader and writer, aggregations, updates, equi, non-equi, rolling, range and interval joins, in a short and flexible syntax, for faster development. It is inspired by A[B] syntax in R where A is a matrix and B is a 2-column matrix. Since a data. table is a data.
A column can be added to an existing data table using := operator. Here ':' represents the fixed values and '=' represents the assignment of values. So, they together represent the assignment of fixed values. Therefore, with the help of “:=” we will add 2 columns in the above table.
Data. table is an extension of data. frame package in R. It is widely used for fast aggregation of large datasets, low latency add/update/remove of columns, quicker ordered joins, and a fast file reader.
Feature has been added to 1.12.0 when subset was made parallel by Matt. So attributes are now being retained.
library(data.table)
my_dt <- data.table(col1 = rnorm(20), col2 = letters[1:20])
attr(my_dt, 'title') <- 'This is my data.table'
attr(my_dt, 'title')
#[1] "This is my data.table"
attr(my_dt[order(col1)], 'title')
#[1] "This is my data.table"
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