Platform: W10-64bit, 4 core, 500GB SSD, 32GB Ram
File to import description: 80MB, contains comma delimited numbers and short character arrays. Overall format 27 columns x 400K lines.
Clicking the import data tool icon prompts for a file name, shows a message "Opening a large text file ..." and then displays the file contents in a table format on the GUI after ~5 seconds. The table displayed matches the file contents.
On the same GUI I set the output type to cell array and range to A2:AA395201 (entire file minus header line). Clicking the Import Selection button displays message "Importing Data..." and a status bar that stays gray for 35 minutes before it suddenly disappears. At that point the import is complete and the variable name appears in the workspace.
Why does the initial opening large text file finish in 5 seconds but the import take 35 minutes? It seems for the opening large text file step to complete and display the data in the GUI table, it has essentially imported the data but 500X faster!