How do I make a list of data frames?
This isn't related to your question, but you want to use =
and not <-
within the function call. If you use <-
, you'll end up creating variables y1
and y2
in whatever environment you're working in:
d1 <- data.frame(y1 <- c(1, 2, 3), y2 <- c(4, 5, 6))
y1
# [1] 1 2 3
y2
# [1] 4 5 6
This won't have the seemingly desired effect of creating column names in the data frame:
d1
# y1....c.1..2..3. y2....c.4..5..6.
# 1 1 4
# 2 2 5
# 3 3 6
The =
operator, on the other hand, will associate your vectors with arguments to data.frame
.
As for your question, making a list of data frames is easy:
d1 <- data.frame(y1 = c(1, 2, 3), y2 = c(4, 5, 6))
d2 <- data.frame(y1 = c(3, 2, 1), y2 = c(6, 5, 4))
my.list <- list(d1, d2)
You access the data frames just like you would access any other list element:
my.list[[1]]
# y1 y2
# 1 1 4
# 2 2 5
# 3 3 6
Correlations between dataframe and list of dataframes in R
You could use lapply
in combination with mapply
to apply cor.test
and extract a specific value from the test. For example, to get p.value
and estimate
we can do
lapply(2:4, function(i) mapply(function(x, y) {
a <- cor.test(x, y, method = "spearman")
c(setNames(a$p.value, "pvalue"), a$estimate)
}, lapply(df2, "[[", i), df1[i]))
Convert a list to a data frame
Update July 2020:
The default for the parameter stringsAsFactors
is now default.stringsAsFactors()
which in turn yields FALSE
as its default.
Assuming your list of lists is called l
:
df <- data.frame(matrix(unlist(l), nrow=length(l), byrow=TRUE))
The above will convert all character columns to factors, to avoid this you can add a parameter to the data.frame() call:
df <- data.frame(matrix(unlist(l), nrow=132, byrow=TRUE),stringsAsFactors=FALSE)
How to subset a list of data.frames?
If we want to subset the list
elements based on names
mainlist_new <- lapply(mainlist, `[`, c("rainfall", "yield"))
-output
> str(mainlist_new)
List of 2
$ :List of 2
..$ rainfall:'data.frame': 5 obs. of 3 variables:
.. ..$ station : chr [1:5] "MADA1" "MADA2" "MADA3" "MADA4" ...
.. ..$ rainfall: num [1:5] 0 5 10 15 20
.. ..$ yield : num [1:5] 2000 3000 4000 5000 6000
..$ yield :'data.frame': 5 obs. of 3 variables:
.. ..$ station : chr [1:5] "MADA1" "MADA2" "MADA3" "MADA4" ...
.. ..$ rainfall: num [1:5] 0 5 10 15 20
.. ..$ yield : num [1:5] 2000 3000 4000 5000 6000
$ :List of 2
..$ rainfall:'data.frame': 5 obs. of 3 variables:
.. ..$ station : chr [1:5] "MADA1" "MADA2" "MADA3" "MADA4" ...
.. ..$ rainfall: num [1:5] 0 5 10 15 20
.. ..$ yield : num [1:5] 2000 3000 4000 5000 6000
..$ yield :'data.frame': 5 obs. of 3 variables:
.. ..$ station : chr [1:5] "MADA1" "MADA2" "MADA3" "MADA4" ...
.. ..$ rainfall: num [1:5] 0 5 10 15 20
.. ..$ yield : num [1:5] 2000 3000 4000 5000 6000
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