Problem columns

Joining Data with data.table in R

Scott Ritchie

Postdoctoral Researcher in Systems Genomics

Common column names

Using the data.table syntax

parents[children, on = .(name = parent)]

    name gender age    i.name i.gender i.age
1: Sarah      F  41    Oliver        M     5
2:   Max      M  43 Sebastian        M     8
3:   Qin      F  36   Kai-lee        F     7

Common column names with merge()

Using the merge() function

merge(x = children, y = parents, by.x = "parent", by.y = "name")

   parent      name gender.x age.x gender.y age.y
1:    Max Sebastian        M     8        M    43
2:    Qin   Kai-lee        F     7        F    36
3:  Sarah    Oliver        M     5        F    41

Adding context with your own suffixes

The suffixes argument can add useful context:

merge(children, parents, by.x = "parent", by.y = "name", 
      suffixes = c(".child", ".parent"))

   parent      name gender.child age.child gender.parent age.parent
1:    Max Sebastian            M         8             M         43
2:    Qin   Kai-lee            F         7             F         36
3:  Sarah    Oliver            M         5             F         41

Renaming columns

Rename all columns using setnames()

setnames(parents, c("parent", "parent.gender", "parent.age"))

setnames(parents, old = c("gender", "age"), 
         new = c("parent.gender", "parent.age"))

parents

   parent parent.gender parent.age
1:  Sarah             F         41
2:    Max             M         43
3:    Qin             F         36

Joining with `data.frames`

Join keys for data.frames may be in the rownames

parents

      gender age
Sarah      F  41
Max        M  43
Qin        F  36

parents <- as.data.table(parents, keep.rownames = "parent")
parents

   parent gender age
1:  Sarah      F  41
2:    Max      M  43
3:    Qin      F  36

Let's practice!

Joining Data with data.table in R