How to extract data from list in R with each list has multiple entries?

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A simple question: How to extract multiple data from lists with multiple entries.

> data
[[1]]
a     b     p     d     e     f     g     h     i     j     k     l     m     n
0.1  0.2   0.3   0.4   0.5   0.6   0.7   0.8   0.9   1.0   1.1   1.2   1.3   1.4

[[2]]
a     b     p     d     e     f     g     h     i     j     k     l     m     n
0.4  0.2   0.5   0.4   0.8   1.6   0.5   0.8   0.1   1.9   1.3   2.2   1.3   1.4

[[3]]
a     b     p     d     e     f     g     h     i     j     k     l     m     n
0.6  0.8   2.3   3.4   1.5   2.6   1.7   1.8   0.8   1.5   1.0   1.0   1.4   1.6

[[4]]
a     b     p     d     e     f     g     h     i     j     k     l     m     n
0.5  0.1   0.8   1.4   1.5   1.6   2.7   0.8   0.9   1.9   1.2   1.3   1.5   1.0

There are actually 1000 lists (only shown 4 for simplicity). The a, b, p, ..., n are actually names that I have given in another function which returns

return(c("a" = a, "b" = b, ..., "n" = n))

How do I extract so that I will get the following results

#For a values
> data$a
0.1   0.4   0.6   0.5

#For b values
> data$b
0.2   0.2   0.8   0.1

I am also open to changing the list to matrices or vectors and then extracting them. Any method that works are welcome. Thank you.

list r
2 Answers

First provide the data in reproducible format using dput(data):

dput(data)
list(structure(list(a = 0.1, b = 0.2, p = 0.3, d = 0.4, e = 0.5, 
    f = 0.6, g = 0.7, h = 0.8, i = 0.9, j = 1, k = 1.1, l = 1.2, 
    m = 1.3, n = 1.4), row.names = 1L, class = "data.frame"), 
    structure(list(a = 0.4, b = 0.2, p = 0.5, d = 0.4, e = 0.8, 
        f = 1.6, g = 0.5, h = 0.8, i = 0.1, j = 1.9, k = 1.3, 
        l = 2.2, m = 1.3, n = 1.4), row.names = 2L, class = "data.frame"), 
    structure(list(a = 0.6, b = 0.8, p = 2.3, d = 3.4, e = 1.5, 
        f = 2.6, g = 1.7, h = 1.8, i = 0.8, j = 1.5, k = 1, l = 1, 
        m = 1.4, n = 1.6), row.names = 3L, class = "data.frame"), 
    structure(list(a = 0.5, b = 0.1, p = 0.8, d = 1.4, e = 1.5, 
        f = 1.6, g = 2.7, h = 0.8, i = 0.9, j = 1.9, k = 1.2, 
        l = 1.3, m = 1.5, n = 1), row.names = 4L, class = "data.frame"))

Since the data consist of rows of data with the same columns, the simplest approach would be to convert to a matrix:

data.mat <- do.call(rbind, data)
#     a   b   p   d   e   f   g   h   i   j   k   l   m   n
# 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4
# 2 0.4 0.2 0.5 0.4 0.8 1.6 0.5 0.8 0.1 1.9 1.3 2.2 1.3 1.4
# 3 0.6 0.8 2.3 3.4 1.5 2.6 1.7 1.8 0.8 1.5 1.0 1.0 1.4 1.6
# 4 0.5 0.1 0.8 1.4 1.5 1.6 2.7 0.8 0.9 1.9 1.2 1.3 1.5 1.0
data.mat$a
# [1] 0.1 0.4 0.6 0.5

You can also work directly with the list:

sapply(data, "[[", "a")
# 0.1 0.4 0.6 0.5
dcarlson0

How about this, first using (base) lapply and then map from the purrr package:

data <- list(
  x = c(a = 0.1, b = 0.2),
  y = c(a = 0.4, b = 0.2)
)
lapply(data, '[[', 1)
lapply(data, '[[', "a")

library(purrr)
map(data, `[[`, 1)
Paul van Oppen0
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