[英]Why doesn't `pivot_wider` work on a `data.table`
A simple example of long to wide pivot:长到宽 pivot 的简单示例:
library(tidyverse)
library(data.table)
df <- data.frame(names=letters[1:3],values=1:3)
df %>% pivot_wider(names_from=names,values_from=values)
#works
dt <- data.table(names=letters[1:3],values=1:3)
dt %>% pivot_wider(names_from=names,values_from=values)
Error in data.frame(row = row_id, col = col_id) :
arguments imply differing number of rows: 0, 3
Why does this error happen?为什么会发生此错误?
PS: one fix is to remove the data tableness with as.data.frame(dt)
. PS:一种解决方法是使用
as.data.frame(dt)
删除数据表。
dt %>% as.data.frame %>% pivot_wider(names_from=names,values_from=values)
#works
Manual entry of this function in tidyr
mentions only "data frame" without specifying other classes like tibble or data.table.在
tidyr
中手动输入此 function 仅提及“数据框”,而未指定其他类,如 tibble 或 data.table。 So addressing your question, function is either not designed to handle data.table, or there is a bug in pivot_wider
.因此,解决您的问题,function 不是设计用于处理 data.table,或者在
pivot_wider
中存在错误。
As a workaround you can now use as.data.frame
(as you already mentioned), if your data is big then possibly setDF
to avoid extra in-memory copy.作为一种解决方法,您现在可以使用
as.data.frame
(正如您已经提到的),如果您的数据很大,那么可能setDF
以避免额外的内存复制。
You can also use data.table
function dcast
to perform same kind of transformation.您还可以使用
data.table
function dcast
执行相同类型的转换。
library(tidyr)
library(data.table)
df <- data.frame(names=letters[1:3],values=1:3)
pivot_wider(df, names_from=names,values_from=values)
## A tibble: 1 x 3
# a b c
# <int> <int> <int>
#1 1 2 3
setDT(df)
dcast(df, .~names, value.var="values")[, ".":=NULL][]
# a b c
#1: 1 2 3
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