I have a list of data.frames that looks like this:
df=data.frame(
data_id=rep(LETTERS[1:10],each=1),
data_value=c(1,2,2,3,3,2,3,1,1,3))
df2=data.frame(
data_id=rep(LETTERS[1:10],each=1),
data_value=c(2,1,3,1,1,1,2,1,2,1))
df3=data.frame(
data_id=rep(LETTERS[1:10],each=1),
data_value=c(2,2,3,3,1,2,2,1,2,3))
df.list <- list(df, df2, df3)
A single data.frame looks like this:
data_id data_value
1 A 1
2 B 2
3 C 2
4 D 3
5 E 3
6 F 2
7 G 3
8 H 1
9 I 1
10 J 3
I want to have a frequency count of how often each unique value appears in data_value. I can do this:
for(i in 1:length(df.list)){
daply(df.list[[i]], .(df.list[[i]]$data_value), nrow) -> freq
}
Which gives me the frequency count (in this case just the last one, for df3):
1 2 3
2 5 3
My actual dataset is far bigger so I cannot post it here. It has the exact same structure, however. The problem is that when I try to get the frequency counts for my actual dataset, I get the following error message:
Error in dim(out_array) <- out_dim : dims [product 0] do not match the length of object [1]
Can anyone tell me where I need to start looking to fix this? I don't understand where 'dim()' comes in and what it does. Many thanks.
You can actually do one better than that, by replacing the for-loop with a laply
, which means input is a list and output is a matrix/array.
o <- laply(df.list, function(x) {
table(x$data_value)
})
> o
# 1 2 3
# [1,] 3 3 4
# [2,] 6 3 1
# [3,] 2 5 3
In order to check the reason for your error, what happens when you try this?
o <- llply(df.list, function(x) {
table(x$data_value)
})
Edit: To make the error more understandable, let us create this data.frame:
d1 <- data.frame(a=1:4)
d2 <- data.frame(a=1:5)
d3 <- data.frame(a=1:6)
d4 <- data.frame(a=1:7)
dl <- list(d1,d2,d3,d4)
Now run laply
:
laply(dl, function(x) table(x$a))
# Error: Results must have the same dimensions.
why? To see that, let's print it:
> laply(dl, function(x) print(table(x$a)))
# 1 2 3 4
# 1 1 1 1
#
# 1 2 3 4 5
# 1 1 1 1 1
#
# 1 2 3 4 5 6
# 1 1 1 1 1 1
#
# 1 2 3 4 5 6 7
# 1 1 1 1 1 1 1
# Error: Results must have the same dimensions.
You see the problem? The number of elements in each row are different. You can NOT have a matrix (unless you append those with smaller elements to equal the rows).
Instead, use a list so that they will be elements of a list which can be accessed later using [[number]]
syntax.
llply(dl, function(x) table(x$a))
# [[1]]
#
# 1 2 3 4
# 1 1 1 1
#
# [[2]]
#
# 1 2 3 4 5
# 1 1 1 1 1
#
# [[3]]
#
# 1 2 3 4 5 6
# 1 1 1 1 1 1
#
# [[4]]
#
# 1 2 3 4 5 6 7
# 1 1 1 1 1 1 1
Hope this clears things up.
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