Insert or print a column name inside a data table call

Question

I have a rather simple problem as it seems, which I cannot solve myself however.

Can I somehow insert or print a column name within a data table call? I have something like this in mind:

col_names = c("column1","column2")
for (col in col_names){
        datatable$col ...
}

or

col_names = c("column1","column2")
for (col in col_names){
        datatable[,col] ...
}

What I eventually would like to do is transform the variables of certain columns into ordered factors. Since there are many columns, I'm looking for a neater way as an alternative of just coding the same line 20 times with the only difference being the column name.

Thank you for your answer! Yeah, I'm not just trying to print them. I just edited my question to add more detail. Sorry for the insufficient specification. — laser.p, Jul 21 '20 at 14:26

score 0 · Answer 1 · answered Jul 21 '20 at 14:15

0

Are you trying to print the just the column name or the entire column within the datatable?

You could try something like this

col_names = c("column1","column2")
for (i in seq_along(col_names)){
        print(datatable[col_names[[i]]])
}

Or if you just want the names printed.

col_names = c("column1","column2")
for (i in seq_along(col_names)){
        print(col_names[[i]])
}

Also, you might want to check out the iteration chapter in R for Data Science.

answered Jul 21 '20 at 14:15

Abeaver

3
1

Thank you for your answer! Sorry, I might need to specify this in my question. But no, I actually want to perform transformations on the single columns and not just print them. – laser.p Jul 21 '20 at 14:23
Oh! Well then I would absolutely use tidyverse and purr functions for that. You can use ```map()``` from purr to perform functions across multiple columns. – Abeaver Jul 21 '20 at 14:33

score 0 · Answer 2 · answered Jul 21 '20 at 14:27

Perhaps, you can try lapply with SDcols to apply a function over col_names. You can try something like this :=

library(data.table)
datatable[, (col_names) := lapply(.SD, function(x) factor(x, ordered =  TRUE)), 
             .SDcols = col_names]

Here we apply factor(x, ordered = TRUE) to each column in col_names where x is each individual column name.

Insert or print a column name inside a data table call

2 Answers2