命名列表到/从 Data.Frame [英] Named List To/From Data.Frame
问题描述
I'm looking for a quick way to get back and forth between a list of the following format:
$`a`
[1] 1 2 3
$`b`
[1] 4 5 6
to/from a data.frame of the following format:
name x
1 a 1
2 a 2
3 a 3
4 b 4
5 b 5
6 b 6
(Don't really care what the names of the columns are, in this case.)
Here's the data frame used above in R-format:
df <- data.frame(name=c(rep("a",3),rep("b",3)), x=c(1:3,4:6))
Again, I'm looking for two separate operations: one to convert the above data.frame to a list, and another to convert it back to a data.frame.
Use stack
and unstack
in base R:
x <- data.frame(a=1:3, b=4:6)
x
a b
1 1 4
2 2 5
3 3 6
Use stack
to from wide to tall, i.e. stack the vectors on top of one another.
y <- stack(x)
y
values ind
1 1 a
2 2 a
3 3 a
4 4 b
5 5 b
6 6 b
Use unstack
to do the reverse.
unstack(y)
a b
1 1 4
2 2 5
3 3 6
If your data structure is more complicated than you described, stack
and unstack
may no longer be suitable. In that case you'll have to use reshape
in base R, or melt
and dcast
in package reshape2
.
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