Search, match, and look up values (like Excel's functions INDEX + MATCH).

In Excel, we can use VLOOKUP, HLOOKUP, XLOOKUP (a new function released in 2019), or the combination of INDEX and MATCH to search, match, and look up values. Here I provide a similar function. If multiple values were simultaneously matched, a warning message would be printed.

Usage

LOOKUP(
  data,
  vars,
  data.ref,
  vars.ref,
  vars.lookup,
  return = c("new.data", "new.var", "new.value")
)

Arguments

data

Main data.

vars

Character (vector), specifying the variable(s) to be searched in data.

data.ref

Reference data containing both the reference variable(s) and the lookup variable(s).

vars.ref

Character (vector), with the same length and order as vars, specifying the reference variable(s) to be matched in data.ref.

vars.lookup

Character (vector), specifying the variable(s) to be looked up and returned from data.ref.

return

What to return. Default ("new.data") is to return a data frame with the lookup values added. You may also set it to "new.var" or "new.value".

Value

New data object, new variable, or new value (see the argument return).

See also

dplyr::left_join()

Examples

ref = data.table(City=rep(c("A", "B", "C"), each=5),
                 Year=rep(2013:2017, times=3),
                 GDP=sample(1000:2000, 15),
                 PM2.5=sample(10:300, 15))
ref
#>       City  Year   GDP PM2.5
#>     <char> <int> <int> <int>
#>  1:      A  2013  1439    36
#>  2:      A  2014  1275   102
#>  3:      A  2015  1827    52
#>  4:      A  2016  1879   128
#>  5:      A  2017  1564   115
#>  6:      B  2013  1988   286
#>  7:      B  2014  1456   183
#>  8:      B  2015  1450   150
#>  9:      B  2016  1258    85
#> 10:      B  2017  1203    37
#> 11:      C  2013  1286   190
#> 12:      C  2014  1739   243
#> 13:      C  2015  1015   175
#> 14:      C  2016  1689    91
#> 15:      C  2017  1814   203

data = data.table(sub=1:5,
                  city=c("A", "A", "B", "C", "C"),
                  year=c(2013, 2014, 2015, 2016, 2017))
data
#>      sub   city  year
#>    <int> <char> <num>
#> 1:     1      A  2013
#> 2:     2      A  2014
#> 3:     3      B  2015
#> 4:     4      C  2016
#> 5:     5      C  2017

LOOKUP(data, c("city", "year"), ref, c("City", "Year"), "GDP")
#>      sub   city  year   GDP
#>    <int> <char> <num> <int>
#> 1:     1      A  2013  1439
#> 2:     2      A  2014  1275
#> 3:     3      B  2015  1450
#> 4:     4      C  2016  1689
#> 5:     5      C  2017  1814
LOOKUP(data, c("city", "year"), ref, c("City", "Year"), c("GDP", "PM2.5"))
#>      sub   city  year   GDP PM2.5
#>    <int> <char> <num> <int> <int>
#> 1:     1      A  2013  1439    36
#> 2:     2      A  2014  1275   102
#> 3:     3      B  2015  1450   150
#> 4:     4      C  2016  1689    91
#> 5:     5      C  2017  1814   203