How do I get a contingency table?

Question

I am trying to create a contingency table from a particular type of data. This would be doable with loops etc... but because my final table would contain more than 10E5 cell

Answer 1

With dplyr / tidyr:

df <- read.table(text='PLANT                  ANIMAL                          INTERACTIONS
                 Tragopogon_pratensis   Propylea_quatuordecimpunctata         1
                 Anthriscus_sylvestris  Rhagonycha_nigriventris               3
                 Anthriscus_sylvestris  Sarcophaga_carnaria                   2
                 Heracleum_sphondylium  Sarcophaga_carnaria                   1
                 Anthriscus_sylvestris  Sarcophaga_variegata                  4
                 Anthriscus_sylvestris  Sphaerophoria_interrupta_Gruppe       3
                 Cerastium_holosteoides Sphaerophoria_interrupta_Gruppe       1', header=TRUE)
library(dplyr)
library(tidyr)
df %>% spread(ANIMAL, INTERACTIONS, fill=0)

#                    PLANT Propylea_quatuordecimpunctata Rhagonycha_nigriventris Sarcophaga_carnaria Sarcophaga_variegata Sphaerophoria_interrupta_Gruppe
# 1  Anthriscus_sylvestris                             0                       3                   2                    4                               3
# 2 Cerastium_holosteoides                             0                       0                   0                    0                               1
# 3  Heracleum_sphondylium                             0                       0                   1                    0                               0
# 4   Tragopogon_pratensis                             1                       0                   0                    0                               0