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

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.

CodePudding user response：

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

CodePudding user response：

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)