R: Check if value from dataframe is within range other dataframe

Question

I am looking for a way to look up infromation from 1 dataframe in another dataframe, get a value from that other dataframe and pass it back to the first frame..

exam

Answer 1

Here's a simple base method that uses the OP's logic:

f <- function(vec, id) {
  if(length(.x <- which(vec >= x$from & vec <= x$to & id == x$number))) .x else NA
}
y$name <- x$name[mapply(f, y$location, y$id_number)]
y
#  location id_number     name
#1      1.5        30 region 1
#2      2.8        30 region 2
#3     10.0        38     <NA>
#4      3.5        40     <NA>
#5      2.0        36 region 7

Answer 2

Another base method (mostly):

# we need this for the last line - if you don't use magrittr, just wrap the sapply around the lapply
library(magrittr)

# get a list of vectors where each item is whether an item's location in y is ok in each to/from in x
locationok  <- lapply(y$location, function(z) z >= x$from & z <= x$to)

# another list of logical vectors indicating whether y's location matches the number in x
idok  <- lapply(y$id_number, function(z) z== x$number)

# combine the two list and use the combined vectors as an index on x$name
lapply(1:nrow(y), function(i) {
      x$name[ locationok[[i]] & idok[[i]]  ]
}) %>% 
# replace zero length strings with NA values
sapply( function(x) ifelse(length(x) == 0, NA, x)

Answer 3

Since you want to match the columns of id_number and number, you can join x and y on the columns and then mutate the name to NA if the location doesn't fall between from and to, here is a dplyr option:

library(dplyr)
y %>% left_join(x, by = c("id_number" = "number")) %>% 
      mutate(name = if_else(location >= from & location <= to, as.character(name), NA_character_)) %>% 
      select(-from, -to) %>% arrange(name) %>% 
      distinct(location, id_number, .keep_all = T)

#   location id_number     name
# 1      1.5        30 region 1
# 2      2.8        30 region 2
# 3      2.0        36 region 7
# 4     10.0        38     <NA>
# 5      3.5        40     <NA>