Home >Database >Mysql Tutorial >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.
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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