Working with tables

One of the common ways of seeing data in Nu is through a table. Nu comes with a number of commands for working with tables to make it convenient to find what you're looking for, and for narrowing down the data to just what you need.

To start off, let's get a table that we can use:

> ls
───┬───────────────┬──────┬─────────┬────────────
 # │ name          │ type │ size    │ modified
───┼───────────────┼──────┼─────────┼────────────
 0 files.rs File  4.6 KB 5 days ago
 1 lib.rs File   330 B 5 days ago
 2 lite_parse.rs File  6.3 KB 5 days ago
 3 parse.rs File 49.8 KB 1 day ago
 4 path.rs File  2.1 KB 5 days ago
 5 shapes.rs File  4.7 KB 5 days ago
 6 signature.rs File  1.2 KB 5 days ago
───┴───────────────┴──────┴─────────┴────────────

Changing how tables are displayed

Nu will try to expands all table's structure by default. You can change this behavior by changing the display_output hook. See hooks for more information.

Sorting the data

We can sort a table by calling the sort-by command and telling it which columns we want to use in the sort. Let's say we wanted to sort our table by the size of the file:

> ls | sort-by size
───┬───────────────┬──────┬─────────┬────────────
 # │ name          │ type │ size    │ modified
───┼───────────────┼──────┼─────────┼────────────
 0 lib.rs File   330 B 5 days ago
 1 signature.rs File  1.2 KB 5 days ago
 2 path.rs File  2.1 KB 5 days ago
 3 files.rs File  4.6 KB 5 days ago
 4 shapes.rs File  4.7 KB 5 days ago
 5 lite_parse.rs File  6.3 KB 5 days ago
 6 parse.rs File 49.8 KB 1 day ago
───┴───────────────┴──────┴─────────┴────────────

We can sort a table by any column that can be compared. For example, we could also have sorted the above using the "name", "accessed", or "modified" columns.

Selecting the data you want

We can select data from a table by choosing to select specific columns or specific rows. Let's select a few columns from our table to use:

> ls | select name size
───┬───────────────┬─────────
 # │ name          │ size
───┼───────────────┼─────────
 0 files.rs  4.6 KB
 1 lib.rs   330 B
 2 lite_parse.rs  6.3 KB
 3 parse.rs 49.8 KB
 4 path.rs  2.1 KB
 5 shapes.rs  4.7 KB
 6 signature.rs  1.2 KB
───┴───────────────┴─────────

This helps to create a table that's more focused on what we need. Next, let's say we want to only look at the 5 smallest files in this directory:

> ls | sort-by size | first 5
───┬──────────────┬──────┬────────┬────────────
 # │ name         │ type │ size   │ modified
───┼──────────────┼──────┼────────┼────────────
 0 lib.rs File  330 B 5 days ago
 1 signature.rs File 1.2 KB 5 days ago
 2 path.rs File 2.1 KB 5 days ago
 3 files.rs File 4.6 KB 5 days ago
 4 shapes.rs File 4.7 KB 5 days ago
───┴──────────────┴──────┴────────┴────────────

You'll notice we first sort the table by size to get to the smallest file, and then we use the first 5 to return the first 5 rows of the table.

You can also skip rows that you don't want. Let's skip the first two of the 5 rows we returned above:

> ls | sort-by size | first 5 | skip 2
───┬───────────┬──────┬────────┬────────────
 # │ name      │ type │ size   │ modified
───┼───────────┼──────┼────────┼────────────
 0 path.rs File 2.1 KB 5 days ago
 1 files.rs File 4.6 KB 5 days ago
 2 shapes.rs File 4.7 KB 5 days ago
───┴───────────┴──────┴────────┴────────────

We've narrowed it to three rows we care about.

Let's look at a few other commands for selecting data. You may have wondered why the rows of the table are numbers. This acts as a handy way to get to a single row. Let's sort our table by the file name and then pick one of the rows with the select command using its row number:

> ls | sort-by name
───┬───────────────┬──────┬─────────┬────────────
 # │ name          │ type │ size    │ modified
───┼───────────────┼──────┼─────────┼────────────
 0 files.rs File  4.6 KB 5 days ago
 1 lib.rs File   330 B 5 days ago
 2 lite_parse.rs File  6.3 KB 5 days ago
 3 parse.rs File 49.8 KB 1 day ago
 4 path.rs File  2.1 KB 5 days ago
 5 shapes.rs File  4.7 KB 5 days ago
 6 signature.rs File  1.2 KB 5 days ago
───┴───────────────┴──────┴─────────┴────────────

> ls | sort-by name | select 5
───┬───────────────┬──────┬─────────┬────────────
 # │ name          │ type │ size    │ modified
───┼───────────────┼──────┼─────────┼────────────
 0 shapes.rs File  4.7 KB 5 days ago
───┴───────────────┴──────┴─────────┴────────────

Getting data out of a table

So far, we've worked with tables by trimming the table down to only what we need. Sometimes we may want to go a step further and only look at the values in the cells themselves rather than taking a whole column. Let's say, for example, we wanted to only get a list of the names of the files. For this, we use the get command:

> ls | get name
───┬───────────────
 0 files.rs
 1 lib.rs
 2 lite_parse.rs
 3 parse.rs
 4 path.rs
 5 shapes.rs
 6 signature.rs
───┴───────────────

We now have the values for each of the filenames.

This might look like the select command we saw earlier, so let's put that here as well to compare the two:

> ls | select name
───┬───────────────
 # │ name
───┼───────────────
 0 files.rs
 1 lib.rs
 2 lite_parse.rs
 3 parse.rs
 4 path.rs
 5 shapes.rs
 6 signature.rs
───┴───────────────

These look very similar! Let's see if we can spell out the difference between these two commands to make it clear:

  • select - creates a new table which includes only the columns specified
  • get - returns the values inside the column specified as a list

TIP

The arguments provided to select and get are cell paths, a fundamental part of Nu's query language. In addition to simple queries like get name, you can also do things like get name? (will replace missing values with null instead of returning an error) or get some.deeply.nested.column for nested data.

Changing data in a table

In addition to selecting data from a table, we can also update what the table has. We may want to combine tables, add new columns, or edit the contents of a cell. In Nu, rather than editing in place, each of the commands in the section will return a new table in the pipeline.

Concatenating Tables

We can concatenate tables using append:

let first = [[a b]; [1 2]]
let second = [[a b]; [3 4]]
$first | append $second
───┬───┬───
 # │ a │ b
───┼───┼───
 0 1 2
 1 3 4
───┴───┴───

If the column names are not identical then additionally columns and values will be created as necessary:

let first = [[a b]; [1 2]]
let second = [[a b]; [3 4]]
let third = [[a c]; [3 4]]
$first | append $second | append $third
───┬───┬────┬────
 # │ a │ b  │ c
───┼───┼────┼────
 0 1  2
 1 3  4
 2 3  4
───┴───┴────┴────

You can also use the ++ operator as an inline replacement for append:

$first ++ $second ++ $third
───┬───┬────┬────
 # │ a │ b  │ c
───┼───┼────┼────
 0 1  2
 1 3  4
 2 3  4
───┴───┴────┴───

Merging Tables

We can use the merge command to merge two (or more) tables together

let first = [[a b]; [1 2]]
let second = [[c d]; [3 4]]
$first | merge $second
───┬───┬───┬───┬───
 # │ a │ b │ c │ d
───┼───┼───┼───┼───
 0 1 2 3 4
───┴───┴───┴───┴───

Let's add a third table:

> let third = [[e f]; [5 6]]

We could join all three tables together like this:

> $first | merge $second  | merge $third
───┬───┬───┬───┬───┬───┬───
 # │ a │ b │ c │ d │ e │ f
───┼───┼───┼───┼───┼───┼───
 0 1 2 3 4 5 6
───┴───┴───┴───┴───┴───┴───

Or we could use the reduce command to dynamically merge all tables:

> [$first $second $third] | reduce {|it, acc| $acc | merge $it }
───┬───┬───┬───┬───┬───┬───
 # │ a │ b │ c │ d │ e │ f
───┼───┼───┼───┼───┼───┼───
 0 1 2 3 4 5 6
───┴───┴───┴───┴───┴───┴───

Adding a new column

We can use the insert command to add a new column to the table. Let's look at an example:

> open rustfmt.toml
─────────┬──────
 edition 2018
─────────┴──────

Let's add a column called "next_edition" with the value 2021:

> open rustfmt.toml | insert next_edition 2021
──────────────┬──────
 edition 2018
 next_edition 2021
──────────────┴──────

This visual may be slightly confusing, because it looks like what we've just done is add a row. In this case, remember: rows have numbers, columns have names. If it still is confusing, note that appending one more row will make the table render as expected:

> open rustfmt.toml | insert next_edition 2021 | append {edition: 2021 next_edition: 2024}
───┬─────────┬──────────────
 # │ edition │ next_edition
───┼─────────┼──────────────
 0    2018         2021
 1    2021         2024
───┴─────────┴──────────────

Notice that if we open the original file, the contents have stayed the same:

> open rustfmt.toml
─────────┬──────
 edition 2018
─────────┴──────

Changes in Nu are functional changes, meaning that they work on values themselves rather than trying to cause a permanent change. This lets us do many different types of work in our pipeline until we're ready to write out the result with any changes we'd like if we choose to. Here we could write out the result using the save command:

> open rustfmt.toml | insert next_edition 2021 | save rustfmt2.toml
> open rustfmt2.toml
──────────────┬──────
 edition 2018
 next_edition 2021
──────────────┴──────

Updating a column

In a similar way to the insert command, we can also use the update command to change the contents of a column to a new value. To see it in action let's open the same file:

> open rustfmt.toml
─────────┬──────
 edition 2018
─────────┴──────

And now, let's update the edition to point at the next edition we hope to support:

> open rustfmt.toml | update edition 2021
─────────┬──────
 edition 2021
─────────┴──────

You can also use the upsert command to insert or update depending on whether the column already exists.

Moving columns

You can use move to move columns in the table. For example, if we wanted to move the "name" column from ls after the "size" column, we could do:

> ls | move name --after size
╭────┬──────┬─────────┬───────────────────┬──────────────╮
 #  │ type │  size   │       name        │   modified   │
├────┼──────┼─────────┼───────────────────┼──────────────┤
  0 dir   256 B Applications 3 days ago
  1 dir   256 B Data 2 weeks ago
  2 dir   448 B Desktop 2 hours ago
  3 dir   192 B Disks a week ago
  4 dir   416 B Documents 4 days ago
...

Renaming columns

You can also rename columns in a table by passing it through the rename command. If we wanted to run ls and rename the columns, we can use this example:

> ls | rename filename filetype filesize date
╭────┬───────────────────┬──────────┬──────────┬──────────────╮
 #  │     filename      │ filetype │ filesize │     date     │
├────┼───────────────────┼──────────┼──────────┼──────────────┤
  0 Applications dir    256 B 3 days ago
  1 Data dir    256 B 2 weeks ago
  2 Desktop dir    448 B 2 hours ago
  3 Disks dir    192 B a week ago
  4 Documents dir    416 B 4 days ago
...

Rejecting/Deleting columns

You can also reject columns in a table by passing it through the reject command. If we wanted to run ls and delete the columns, we can use this example:

> ls -l / |reject readonly num_links inode created accessed modified
╭────┬────────┬─────────┬─────────┬───────────┬──────┬───────┬────────╮
  # │  name  │  type   │ target  │   mode    │ uid  │ group │  size  │
├────┼────────┼─────────┼─────────┼───────────┼──────┼───────┼────────┤
  0 /bin symlink usr/bin rwxrwxrwx root root    7 B
  1 /boot dir rwxr-xr-x root root 1.0 KB
  2 /dev dir rwxr-xr-x root root 4.1 KB
  3 /etc dir rwxr-xr-x root root 3.6 KB
  4 /home dir rwxr-xr-x root root   12 B
  5 /lib symlink usr/lib rwxrwxrwx root root    7 B
  6 /lib64 symlink usr/lib rwxrwxrwx root root    7 B
  7 /mnt dir rwxr-xr-x root root    0 B
...
Contributors: Justin Ma, Reilly Wood, Benjamin Kane, D3V1LC0D3R, Darren Schroeder, Hofer-Julian, Ibraheem Ahmed, JT, Joerg Schuetter, Kat Marchán, Lyes Saadi, Máté FARKAS, Reilly Wood, Sam Vente, Sygmei, Tengs-Penkwe, Thanu Poptiphueng, Yethal, Yethal, Zhora Trush, prrao87, pwygab