如何将向量列表放入 dataframe 中？

Question

I'm not sure if the question captures it correctly but I have a dataframe that can be created with the following code

library(dplyr)

counties <- c("aaa", "aaa", "aaa", "bbb", "bbb", "ccc", "ccc", "ccc", "ccc")
zips <- c(1321, 1321, 1322, 1523, 1567, 2102, 2102, 2134, 2140)

example_data <- data.frame(county = counties, zip = zips)

example_data_unique <- example_data %>% 
  select(county, zip) %>% 
  group_by(county, zip) %>% 
  slice(1) %>% 
  ungroup()

My end goal is to create a dataframe/tibble such that each county only appears once and the zip variable is now a vector of all zips in that county. It would look something like this:

county zip

aaa c(1321, 1322)

bbb c(1523, 1567)

Answer 1

We can use split to create a list of unique values

lst1 <- with(unique(example_data), split(zip, county))

---

In dplyr , it can be done with

library(dplyr)
example_data %>%
    distinct %>%
    group_by(county) %>%
    nest

Or wrap with list in summarise

example_data %>%
    distinct %>%
    group_by(county) %>%
    summarise(zip = list(zip))
# A tibble: 3 x 2
#  county zip      
#  <fct>  <list>   
#1 aaa    <dbl [2]>
#2 bbb    <dbl [2]>
#3 ccc    <dbl [3]>

Answer 2

Here is a base R solution using aggregate + unique

dfout <- aggregate(.~county,example_data,unique)

such that

> dfout
  county              zip
1    aaa       1321, 1322
2    bbb       1523, 1567
3    ccc 2102, 2134, 2140