Dynamic adding of columns in R - r

Question

I need some help with finding a good way to dynamically add columns with counts for different categories that I need to extract from a string.
In my data, I have a column that contains names of categories and counts thereof. The fields can be empty or contain any combination of categories one can think of. Here are some examples:
themes:firstcategory_1;secondcategory_33;thirdcategory_5
themes:secondcategory_33;fourthcategory_2
themes:fifthcategory_1
What I need is a column for each category (should have the category's name) and the count extracted from the strings above. The list of categories is dynamic, so I don't know beforehand which ones exist.
How do I approach this?

Answer 1

This code will get a column for each category with the counts for each row.
library(dplyr)
library(tidyr)
library(stringr)
# Create test dataframe
df <- data.frame(themes = c("firstcategory_1;secondcategory_33;thirdcategory_5", "secondcategory_33;fourthcategory_2","fifthcategory_1"), stringsAsFactors = FALSE)
# Get the number of columns to split values into
cols <- max(str_count(df$themes,";")) + 1
# Get vector of temporary column names
cols <- paste0("col",c(1:cols))
df <- df %>%
# Add an ID column based on row number
mutate(ID = row_number()) %>%
# Separate multiple categories by semicolon
separate(col = themes, into = cols, sep = ";", fill = "right") %>%
# Gather categories into a single column
gather_("Column", "Value", cols) %>%
# Drop temporary column
select(-Column) %>%
# Filter out NA values
filter(!is.na(Value)) %>%
# Separate categories from their counts by underscore
separate(col = Value, into = c("Category","Count"), sep = "_", fill = "right") %>%
# Spread categories to create a column for each category, with the count for each ID in that category
spread(Category, Count)