How to create a Markdown table with different column lengths based on a dataframe in long format in R? - r

Question

I'm working on a R Markdown file that I would like to submit as a manuscript to an academic journal. I would like to create a table that shows which three words (item2) co-occur most frequently with some keywords (item1). Note that some key words have more than three co-occurring words. The data that I am currently working with:
item1 <- c("water","water","water","water","water","sun","sun","sun","sun","moon","moon","moon")
item2 <- c("tree","dog","cat","fish","eagle","bird","table","bed","flower","house","desk","tiger")
n <- c("200","83","34","34","34","300","250","77","77","122","46","46")
df <- data.frame(item1,item2,n)
Which gives this dataframe:
item1 item2 n
1 water tree 200
2 water dog 83
3 water cat 34
4 water fish 34
5 water eagle 34
6 sun bird 300
7 sun table 250
8 sun bed 77
9 sun flower 77
10 moon house 122
11 moon desk 46
12 moon tiger 46
Ultimately, I would like to pass the data to the function papaja::apa_table, which requires a data.frame (or a matrix / list). I therefore need to reshape the data.
My question:
How can I reshape the data (preferably with dplyr) to get the following structure?
water_item2 water_n sun_item2 sun_n moon_item2 moon_n
1 tree 200 bird 300 house 122
2 dog 83 table 250 desk 46
3 cat 34 bed 77 tiger 46
4 fish 34 flower 77 <NA> <NA>
5 eagle 34 <NA> <NA> <NA> <NA>

Answer 1

We can borrow an approach from an old answer of mine to a different question, and modify a classic gather(), unite(), spread() strategy by creating unique identifiers by group to avoid duplicate identifiers, then dropping that variable:
library(dplyr)
library(tidyr)
item1 <- c("water","water","water","water","water","sun","sun","sun","sun","moon","moon","moon")
item2 <- c("tree","dog","cat","fish","eagle","bird","table","bed","flower","house","desk","tiger")
n <- c("200","83","34","34","34","300","250","77","77","122","46","46")
# Owing to Richard Telford's excellent comment,
# I use data_frame() (or equivalently for our purposes,
# data.frame(..., stringsAsFactors = FALSE))
# to avoid turning the strings into factors
df <- data_frame(item1,item2,n)
df %>%
group_by(item1) %>%
mutate(id = 1:n()) %>%
ungroup() %>%
gather(temp, val, item2, n) %>%
unite(temp2, item1, temp, sep = '_') %>%
spread(temp2, val) %>%
select(-id)
# A tibble: 5 x 6
moon_item2 moon_n sun_item2 sun_n water_item2 water_n
<chr> <chr> <chr> <chr> <chr> <chr>
1 house 122 bird 300 tree 200
2 desk 46 table 250 dog 83
3 tiger 46 bed 77 cat 34
4 NA NA flower 77 fish 34
5 NA NA NA NA eagle 34