Is there a dictionary functionality in R

Question

Is there a way to create a "dictionary" in R, such that it has pairs? Something to the effect of:

x=dictionary(c("Hi","Why","water") , c(1,5,4)) x["Why"]=5 

I'm asking this because I am actually looking for a two categorial variables function.

So that if x=dictionary(c("a","b"),c(5,2))

     x  val 1    a  5  2    b  2  

I want to compute x1^2+x2 on all combinations of x keys

     x1 x2 val1  val2  x1^2+x2 1    a  a   5     5      30 2    b  a   2     5      9 3    a  b   5     2      27 4    b  b   2     2      6 

And then I want to be able to retrieve the result using x1 and x2. Something to the effect of: get_result["b","a"] = 9

what is the best, efficient way to do this?

Answer 1

I know three R packages for dictionaries: hash, hashmap, and dict.

Update July 2018: a new one, container.

Update September 2018: a new one, collections

hash

Keys must be character strings. A value can be any R object.

library(hash) ## hash-2.2.6 provided by Decision Patterns h <- hash()  # set values h[["1"]] <- 42 h[["foo"]] <- "bar" h[["4"]] <- list(a=1, b=2) # get values h[["1"]] ## [1] 42 h[["4"]] ## $a ## [1] 1 ##  ## $b ## [1] 2 h[c("1", "foo")] ## <hash> containing 2 key-value pair(s). ##   1 : 42 ##   foo : bar h[["key not here"]] ## NULL 

To get keys:

keys(h) ## [1] "1"   "4"   "foo" 

To get values:

values(h) ## $`1` ## [1] 42 ##  ## $`4` ## $`4`$a ## [1] 1 ##  ## $`4`$b ## [1] 2 ##  ##  ## $foo ## [1] "bar" 

The print instance:

h ## <hash> containing 3 key-value pair(s). ##   1 : 42 ##   4 : 1 2 ##   foo : bar 

The values function accepts the arguments of sapply:

values(h, USE.NAMES=FALSE) ## [[1]] ## [1] 42 ##  ## [[2]] ## [[2]]$a ## [1] 1 ##  ## [[2]]$b ## [1] 2 ##  ##  ## [[3]] ## [1] "bar" values(h, keys="4") ##   4 ## a 1 ## b 2 values(h, keys="4", simplify=FALSE) ## $`4` ## $`4`$a ## [1] 1 ##  ## $`4`$b ## [1] 2 

hashmap

See https://cran.r-project.org/web/packages/hashmap/README.html.

hashmap does not offer the flexibility to store arbitrary types of objects.

Keys and values are restricted to "scalar" objects (length-one character, numeric, etc.). The values must be of the same type.

library(hashmap) H <- hashmap(c("a", "b"), rnorm(2)) H[["a"]] ## [1] 0.1549271 H[[c("a","b")]] ## [1]  0.1549271 -0.1222048 H[[1]] <- 9 

Beautiful print instance:

H ## ## (character) => (numeric)   ## ##         [1] => [+9.000000] ## ##         [b] => [-0.122205] ## ##         [a] => [+0.154927] 

Errors:

H[[2]] <- "Z" ## Error in x$`[[<-`(i, value): Not compatible with requested type: [type=character; target=double]. H[[2]] <- c(1,3) ## Warning in x$`[[<-`(i, value): length(keys) != length(values)! 

dict

Currently available only on Github: https://github.com/mkuhn/dict

Strengths: arbitrary keys and values, and fast.

library(dict) d <- dict() d[[1]] <- 42 d[[c(2, 3)]] <- "Hello!" # c(2,3) is the key d[["foo"]] <- "bar" d[[4]] <- list(a=1, b=2) d[[1]] ## [1] 42 d[[c(2, 3)]] ## [1] "Hello!" d[[4]] ## $a ## [1] 1 ##  ## $b ## [1] 2 

Accessing to a non-existing key throws an error:

d[["not here"]] ## Error in d$get_or_stop(key): Key error: [1] "not here" 

But there is a nice feature to deal with that:

d$get("not here", "default value for missing key") ## [1] "default value for missing key" 

Get keys:

d$keys() ## [[1]] ## [1] 4 ##  ## [[2]] ## [1] 1 ##  ## [[3]] ## [1] 2 3 ##  ## [[4]] ## [1] "foo" 

Get values:

d$values() ## [[1]] ## [1] 42 ##  ## [[2]] ## [1] "Hello!" ##  ## [[3]] ## [1] "bar" ##  ## [[4]] ## [[4]]$a ## [1] 1 ##  ## [[4]]$b ## [1] 2 

Get items:

d$items() ## [[1]] ## [[1]]$key ## [1] 4 ##  ## [[1]]$value ## [[1]]$value$a ## [1] 1 ##  ## [[1]]$value$b ## [1] 2 ##  ##  ##  ## [[2]] ## [[2]]$key ## [1] 1 ##  ## [[2]]$value ## [1] 42 ##  ##  ## [[3]] ## [[3]]$key ## [1] 2 3 ##  ## [[3]]$value ## [1] "Hello!" ##  ##  ## [[4]] ## [[4]]$key ## [1] "foo" ##  ## [[4]]$value ## [1] "bar" 

No print instance.

The package also provides the function numvecdict to deal with a dictionary in which numbers and strings (including vectors of each) can be used as keys, and that can only store vectors of numbers.

Answer 2

You can use just data.frame and row.names to do this:

x=data.frame(row.names=c("Hi","Why","water") , val=c(1,5,4)) x["Why",] [1] 5