CODEWITHSUNDEEP
r
ChuckCottrill
ChuckCottrill

Reputation: 4444

Replace value from dataframe column with value from keyvalue lookup

I want to replace certain values in a data frame column with values from a lookup table. I have the values in a list, stuff.kv, and many values are stored in the list (but some may not be).

stuff.kv <- list()
stuff.kv[["one"]] <- "thing"
stuff.kv[["two"]] <- "another"
#etc

I have a dataframe, df, which has multiple columns (say 20), with assorted names. I want to replace the contents of the column named 'stuff' with values from 'lookup'.

I have tried building various apply methods, but nothing has worked.

I built a function, which process a list of items and returns the mutated list,

stuff.lookup <- function(x) {
  for( n in 1:length(x) ) {
    if( !is.null( stuff.kv[[x[n]]] ) ) x[n] <- stuff.kv[[x[n]]]
  }
  return( x )
}

unlist(lapply(df$stuff, stuff.lookup))

The apply syntax is bedeviling me.

Upvotes: 1

Views: 619

Answers (2)

ozanstats
ozanstats

Reputation: 2864

Below is a more general solution building on @G5W's answer as it doesn't cover the case where your original data frame has values that don't exist in the lookup table (which would result in length mismatch error):

library(dplyr)

stuff.kv <- list(one = "another", two = "thing")

df <- data_frame(
  stuff = rep(c("one", "two", "three"), each = 3)
)

df <- df %>%
  mutate(stuff = paste(stuff.kv[stuff]))

Upvotes: 1

G5W
G5W

Reputation: 37661

Since you made such a nice lookup table, You can just use it to change the values. No loops or apply needed.

## Sample Data
set.seed(1234)
DF = data.frame(stuff = sample(c("one", "two"), 8, replace=TRUE))

## Make the change
DF$stuff = unlist(stuff.kv[DF$stuff])
DF
    stuff
1   thing
2 another
3 another
4 another
5 another
6 another
7   thing
8   thing

Upvotes: 2

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