如何删除R中data.tables中重复的（按名称）列？

Question

While reading a data set using fread , I've noticed that sometimes I'm getting duplicated column names, for example ( fread doesn't have check.names argument)

> data.table( x = 1, x = 2)
   x x
1: 1 2

The question is: is there any way to remove 1 of 2 columns if they have the same name?

Answer 1

How about

dt[, .SD, .SDcols = unique(names(dt))]

This selects the first occurrence of each name (I'm not sure how you want to handle this).

As @DavidArenburg suggests in comments above, you could use check.names=TRUE in data.table() or fread()

Answer 2

.SDcols approaches would return a copy of the columns you're selecting. Instead just remove those duplicated columns using := , by reference.

dt[, which(duplicated(names(dt))) := NULL]
#    x
# 1: 1

Answer 3

Different approaches:

1. Indexing

   my.data.table <- my.data.table[ ,-2]

2. Subsetting

   my.data.table <- subset(my.data.table, select = -2)

3. Making unique names if 1. and 2. are not ideal (when having hundreds of columns, for instance)

   setnames(my.data.table, make.names(names = names(my.data.table), unique=TRUE))

4. Optionnaly systematize deletion of variables which names meet some criterion (here, we'll get rid of all variables having a name ending with ".X" (X being a number, starting at 2 when using make.names )

   my.data.table <- subset(my.data.table, select = !grepl(pattern = "\\\\.\\\\d$", x = names(my.data.table)))