How Can I Replicate SQL's RANK Functions (ROW_NUMBER, RANK, DENSE_RANK, LEAD, LAG) in R?

Emulating SQL's Rank Functions in R

Rank Function Equivalents in R

The data.table package offers functionality similar to Oracle's SQL rank functions.

• ROW_NUMBER(): Mimicking this function is straightforward.
• RANK(): data.table's rank(x, ties.method = "min") is similar to Oracle's RANK().
• DENSE_RANK(): Convert values to a factor and return integer values to mimic this function.

Rank Function Usage Example

library(data.table)

DT <- data.table(ID = seq_len(4 * 3),
                 group = rep(1:4, each = 3),
                 value = rnorm(4 * 3),
                 info = c(sample(c("a", "b"), 4 * 2, replace = TRUE),
                           sample(c("c", "d"), 4, replace = TRUE)),
                 key = "ID")

DT[, valRank := rank(-value), by = "group"]

DENSE_RANK Mimicry

DT[, infoRank := rank(info, ties.method = "min"), by = "group"]
DT[, infoRankDense := as.integer(factor(info)), by = "group"]

LEAD and LAG Imitation

Create a rank variable based on the order of IDs within groups. Then, use J() to retrieve values from previous or subsequent records.

DT[, idRank := rank(ID), by = "group"]
setkey(DT, group, idRank)

DT[, prev := DT[J(group, idRank - 1), value, mult = 'last']]

For LEAD, add the appropriate offset to idRank and use multi = 'first':

DT[, nex := DT[J(group, idRank + 1), value, mult = 'first']]

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