FAQ?
How do I choose which columns to import into Fread?
Once you know the file structure, you can choose which columns to import. fread’s select option lets you pick columns you want to keep. select takes a vector of either column names or column-position numbers. If names, they need to be in quotation marks, like most vectors of character strings:
How do you read the column types in Fread?
The first 5 rows, middle 5 rows and last 5 rows are then read to determine column types. The lowest type for each column is chosen from the ordered list integer, integer64, double, character. This enables fread to allocate exactly the right number of rows, with columns of the right type, up front once.
Why do we use Fread to allocate rows?
This enables fread to allocate exactly the right number of rows, with columns of the right type, up front once. The file may of course still contain data of a different type in rows other than first, middle and last 5. In that case, the column types are bumped mid read and the data read on previous rows is coerced.
How do I See column names without any data in Fread?
If you just want to see column names without any data at all, you can use nrows = 0 . Once you know the file structure, you can choose which columns to import. fread’s select option lets you pick columns you want to keep. select takes a vector of either column names or column-position numbers.