Removing a List of Columns from a Data.Frame Using Subset

removing a list of columns from a data.frame using subset

I would probably do this like so:

to.remove <- c("hp","drat","wt","qsec")
`%ni%` <- Negate(`%in%`)
subset(mtcars,select = names(mtcars) %ni% to.remove)

(I use %ni% a lot, so I have it built into my .Rprofile already.)

How to drop columns by name in a data frame

You should use either indexing or the subset function. For example :

R> df <- data.frame(x=1:5, y=2:6, z=3:7, u=4:8)
R> df
  x y z u
1 1 2 3 4
2 2 3 4 5
3 3 4 5 6
4 4 5 6 7
5 5 6 7 8

Then you can use the which function and the - operator in column indexation :

R> df[ , -which(names(df) %in% c("z","u"))]
  x y
1 1 2
2 2 3
3 3 4
4 4 5
5 5 6

Or, much simpler, use the select argument of the subset function : you can then use the - operator directly on a vector of column names, and you can even omit the quotes around the names !

R> subset(df, select=-c(z,u))
  x y
1 1 2
2 2 3
3 3 4
4 4 5
5 5 6

Note that you can also select the columns you want instead of dropping the others :

R> df[ , c("x","y")]
  x y
1 1 2
2 2 3
3 3 4
4 4 5
5 5 6

R> subset(df, select=c(x,y))
  x y
1 1 2
2 2 3
3 3 4
4 4 5
5 5 6

Drop data frame columns by name

There's also the subset command, useful if you know which columns you want:

df <- data.frame(a = 1:10, b = 2:11, c = 3:12)
df <- subset(df, select = c(a, c))

UPDATED after comment by @hadley: To drop columns a,c you could do:

df <- subset(df, select = -c(a, c))

How to remove rows from a data frame using a subset?

Data:

df <- data.frame(SFC = c("YU006UGD31092","YU006UGD31071",
                         "YU006UGD30152",
                         "YU006UGD25831",
                         "YU006UGD25831",
                         "YU006UGD25332" ,
                         "YU006UG922912",
                         "YU006UG922912"))

Code:

df %>% 
  group_by(SFC) %>% 
  filter(n() == 1)

Output:

  SFC          
  <chr>        
1 YU006UGD31092
2 YU006UGD31071
3 YU006UGD30152
4 YU006UGD25332

Edit:

If you have the list, you can also do:

df %>% 
  filter(!(SFC %in% Remove_SFC))

Creating a function to remove columns with different names from a list of dataframes

You can try:

#Function
remove_col <- function(df,name){
  vec <- which(names(df) %in% name)
  df = df[,-vec]
  return(df)
}
df_list <- lapply(df_list, remove_col,name=c('X', 'X..x', 'X..y'))

$df1
  var1 var2
1    a    1
2    b    1
3    c    0
4    d    0
5    e    1

$df2
  var1 var2
1    f    0
2    g    1
3    h    0
4    i    1
5    j    1

How do you remove columns from a data.frame?

I use data.table's := operator to delete columns instantly regardless of the size of the table.

DT[, coltodelete := NULL]

or

DT[, c("col1","col20") := NULL]

or

DT[, (125:135) := NULL]

or

DT[, (variableHoldingNamesOrNumbers) := NULL]

Any solution using <- or subset will copy the whole table. data.table's := operator merely modifies the internal vector of pointers to the columns, in place. That operation is therefore (almost) instant.

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