R, select values from data frame column based on matching value in a second column to a vector

Question

I have a data frame like this:

<table>
  <tr><td>Task</td><td>UserStory</td><tr>
  <tr><td>123</td><td>abc</td><tr>
  <tr><td>4321</td><td>abc</td><tr>
  <tr><td>8763</td><td>abc</td><tr>
  <tr><td>9087</td><td>efg</td><tr>
  <tr><td>0652</td><td>efg</td><tr>
  <tr><td>7609</td><td>hij</td><tr>
</table>

I have collected the unique values for User Story into a vector. ("abc", "efg", "hij"). Let's say I've created this vector as "UserStories".

UserStories <- c("abc", "efg", "hij")

I would like to create a vector of matching Tasks for each value in the first vector, with the eventual goal of creating a second data frame with this structure:

<table>
  <tr><td>abc</td><td>1234</td><td>4321</td><td>8763</td><tr>
  <tr><td>efg</td><td>9087</td><td>0652</td><td>NA</td><tr>
  <tr><td>hij</td><td>609</td><td>NA</td><td>NA</td><tr>
</table>

I thinking of then rbind'ing them into a second data frame once I've padded the missing values with NA:

abc, 1234, 4321, 8763 efg, 9087, 0652, NA hij, 7609, NA, NA

I've been googling all afternoon without finding an approach.

I'd like to pass the UserStories vector to a function which would extract a series of vectors for all of the tasks associated with each UserStory.

Thanks in advance to any takers.

Evan Friedland · Accepted Answer · 2017-06-24 02:14:55Z

1

There are much better ways with packages to do this but I always try base R code first:

df <- data.frame(Task = c(123,4321,8763,9087,0652,7609), UserStory = c("abc","abc","abc","efg","efg","hij"))
# Splitting
df.split <- split(df$Task, df$UserStory)
# Combining
maxLength <- max(rapply(df.split, length))
# initialize
new <- list()
z <- NULL # hold the object for length editing to include NAs
for(i in 1:length(df.split)){
  z <- df.split[[i]]
  length(z) <- maxLength # edit the length
  new[[i]] <- c(names(df.split)[i], z)
}
final <- as.data.frame(do.call(rbind,new))
final
#   V1   V2   V3   V4
#1 abc  123 4321 8763
#2 efg 9087  652 <NA>
#3 hij 7609 <NA> <NA>

answered Jun 24, 2017 at 2:14

Evan Friedland

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2 Comments

Charles Knell Over a year ago

Thank you! I, too prefer to use base R. It gives me the illusion that I understand what's going on as compared to using, say, dplyr. I'll get started with your solution.

Evan Friedland Over a year ago

Let me know if you have any questions

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