Q:

How to get the names of the data frames within a list

My list has the following dataframes.  I did not name them when I created the list
str(train_data)
List of 16
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 49.9 53.5 54.4 56 54.4 55.3 57.2 55.8 58.8 58.1 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 4555 5014 4647 5121 6461 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 215 215 216 217 217 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 5399 5374 5560 5517 5386 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 139901 139492 138818 138432 138659 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 117 118 118 118 119 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 0.9 0.4 -0.2 -0.6 -0.7 -0.5 -0.4 -0.2 0.2 0.5 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 119 121 121 122 124 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-01" "2009-08-03" "2009-09-01" ...
  ..$ Value   : num [1:72] 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 411 418 386 396 375 352 345 336 381 422 ...
 $ :'data.frame':   68 obs.  of  2 variables:
  ..$ DateTime: Date[1:68], format: "2009-11-30" "2009-12-31" "2010-01-31" ...
  ..$ Value   : num [1:68] 100 100 101 101 101 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 0.2 1.9 -2.4 1 1 0.4 0 0.2 2.2 0.7 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 14601 14814 15009 15352 15219 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 11.39 14.58 9.38 10.41 10.86 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] -4.43 -4.72 -4.83 -4.81 -3.74 -2.16 -0.6 0.03 1.02 1.36 ...
 $ :'data.frame':   72 obs.  of  2 variables:
  ..$ DateTime: Date[1:72], format: "2009-07-31" "2009-08-31" "2009-09-30" ...
  ..$ Value   : num [1:72] 0 0.3 0.2 0.3 0.3 0.1 0.1 -0.1 0 0 ...

Now I want to create a data frame which will have the first column containing the names of these data frames but I cant seem to find their names.  Should I be naming all the 16 data frames manually (This would not be efficient)  
Thank You.  

A:

If we need to create a column of 'names' for each data.frame in the list (based on the str in OP's post, there are no names for the data.frame, so we can name it by pasteing the 'dat' string with the sequence of train_data), we can use Map to create a column of 'Names' in each of the data.frame
Map(cbind, Names = paste0('dat', seq_along(train_data)), train_data)

Update
If we have used the list.files to get the names of the files, we strip off the .csv part with sub and name the 'train_data' list with that, and use Map
nm1 <- sub("\\.csv", "", temp)
names(train_data) <- nm1
Map(cbind, Names = names(train_data), train_data)

Or just
Map(cbind, Names = nm1, train_data)

