recipes.md

# Recipes

This page includes code snippets or "**recipes**" for a variety of common tasks.
Use them as building blocks or examples when making your own notebooks.

In these recipes, **each code block represents a cell**.

## Control Flow

### Show an output conditionally

**Use cases.** Hide an output until a condition is met (_e.g._, until algorithm
parameters are valid), or show different outputs depending on the value of a UI
element or some other Python object

**Recipe.**

1. Use an `if` expression to choose which output to show.

```python
# condition is a boolean, True of False
condition = True
"condition is True" if condition else None
```

### Run a cell on a timer

**Use cases.**

- Load new data periodically, and show updated plots or other outputs. For
  example, in a dashboard monitoring a training run, experiment trial,
  real-time weather data, ...
- Run a job periodically

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create a [`mo.ui.refresh`](api/inputs/refresh.md#marimo.ui.refresh) timer that fires once a second:

```python
refresh = mo.ui.refresh(default_interval="1s")
# This outputs a timer that fires once a second
refresh
```

3. Reference the timer by name to make this cell run once a second

```python
import random

# This cell will run once a second!
refresh

mo.md("#" + "🍃" * random.randint(1, 10))
```

```{admonition} Requires "on cell change" autorun
:class: note

For this to work, the [runtime configuration's](/guides/configuration/runtime_configuration.md) `on cell change` should be
set to `autorun`
```



### Require form submission before sending UI value

**Use cases.** UI elements automatically send their values to the Python when
they are interacted with, and run all cells referencing the elements. This
makes marimo notebooks responsive, but it can be an issue when the
downstream cells are expensive, or when the input (such as a text box)
needs to be filled out completely before it is considered valid. Forms
let you gate submission of UI element values on manual confirmation, via a
button press.

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create a submittable form.

```python
form = mo.ui.text(label="Your name").form()
form
```

3. Get the value of the form.

```python
form.value
```

### Stop execution of a cell and its descendants

**Use cases.**  For example, don't run a cell or its descendants if a form is
unsubmitted.

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create a submittable form.

```python
form = mo.ui.text(label="Your name").form()
form
```

3. Use [`mo.stop`](api/control_flow.md#marimo.stop) to stop execution when
the form is unsubmitted.

```python
mo.stop(form.value is None, mo.md("Submit the form to continue"))

mo.md(f"Hello, {form.value}!")
```

## Grouping UI elements together

### Create an array of UI elements

**Use cases.** In order to synchronize UI elements between the frontend and
backend (Python), marimo requires you to
[assign UI elements to global variables](guides/interactivity.md).
But sometimes you don't know the number of elements to make until runtime:
for example, maybe you want to make a list of sliders, and the number of sliders
to make depends on the value of some other UI element.

You might be tempted to create a Python list of UI elements,
such as `l = [mo.ui.slider(1, 10) for i in range(number.value)]`: _however,
this won't work, because the sliders are not bound to global variables_.

For such cases, marimo provides the "higher-order" UI element
[`mo.ui.array`](api/inputs/array.md#marimo.ui.array), which lets you make
a new UI element out of a list of UI elements:
`l = mo.ui.array([mo.ui.slider(1, 10) for i in range(number.value)])`.
The value of an `array` element is a list of the values of the elements
it wraps (in this case, a list of the slider values). Any time you interact
with any of the UI elements in the array, all cells referencing the array
by name (in this case, "`l`") will run automatically.

**Recipe.**

1. Import packages.

```python
import marimo as mo
```

2. Use [`mo.ui.array`](api/inputs/array.md#marimo.ui.array) to group together
   many UI elements into a list.

```python
import random

# instead of random.randint, in your notebook you'd use the value of
# an upstream UI element or other Python object
array = mo.ui.array([mo.ui.text() for i in range(random.randint(1, 10))])
array
```

3. Get the value of the UI elements using `array.value`

```python
array.value
```

### Create a dictionary of UI elements

**Use cases.** Same as for creating an array of UI elements, but lets you
name each of the wrapped elements with a string key.

**Recipe.**

1. Import packages.

```python
import marimo as mo
```

2. Use [`mo.ui.dictionary`](api/inputs/dictionary.md#marimo.ui.dictionary) to
   group together many UI elements into a list.

```python
import random

# instead of random.randint, in your notebook you'd use the value of
# an upstream UI element or other Python object
dictionary = mo.ui.dictionary({str(i): mo.ui.text() for i in range(random.randint(1, 10))})
dictionary
```

3. Get the value of the UI elements using `dictionary.value`

```python
dictionary.value
```

### Embed a dynamic number of UI elements in another output

**Use cases.** When you want to embed a dynamic number of UI elements
in other outputs (like tables or markdown).

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Group the elements with
[`mo.ui.dictionary`](#marimo.ui.dictionary) or
[`mo.ui.array`](#marimo.ui.array), then retrieve them from the container
and display them elsewhere.

```python
import random

n_items = random.randint(2, 5)

# Create a dynamic number of elements using `mo.ui.dictionary` and
# `mo.ui.array`
elements = mo.ui.dictionary(
    {
        "checkboxes": mo.ui.array([mo.ui.checkbox() for _ in range(n_items)]),
        "texts": mo.ui.array(
            [mo.ui.text(placeholder="task ...") for _ in range(n_items)]
        ),
    }
)

mo.md(
    f"""
    Here's a TODO list of {n_items} items\n\n
    """
    + "\n\n".join(
        # Iterate over the elements and embed them in markdown
        [
            f"{checkbox} {text}"
            for checkbox, text in zip(
                elements["checkboxes"], elements["texts"]
            )
        ]
    )
)
```

3. Get the value of the elements

```python
elements.value
```

### Create a hstack (or vstack) of UI elements with `on_change` handlers

**Use cases.** Arrange a dynamic number of UI elements in a hstack or vstack,
for example some number of buttons, and execute some side-effect when an
element is interacted with, e.g. when a button is clicked.

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create buttons in `mo.ui.array` and pass them to hstack -- a regular
Python list won't work. Make sure to assign the array to a global variable.

```python
import random


# Create a state object that will store the index of the
# clicked button
get_state, set_state = mo.state(None)

# Create an mo.ui.array of buttons - a regular Python list won't work.
buttons = mo.ui.array(
    [
        mo.ui.button(
            label="button " + str(i), on_change=lambda v, i=i: set_state(i)
        )
        for i in range(random.randint(2, 5))
    ]
)

mo.hstack(buttons)
```

3. Get the state value

```python
get_state()
```

### Create a table column of buttons with `on_change` handlers

**Use cases.** Arrange a dynamic number of UI elements in a column of
a table, and execute some side-effect when an element is interacted with, e.g.
when a button is clicked.

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create buttons in `mo.ui.array` and pass them to `mo.ui.table`.
Make sure to assign the table and array to global variables

```python
import random


# Create a state object that will store the index of the
# clicked button
get_state, set_state = mo.state(None)

# Create an mo.ui.array of buttons - a regular Python list won't work.
buttons = mo.ui.array(
    [
        mo.ui.button(
            label="button " + str(i), on_change=lambda v, i=i: set_state(i)
        )
        for i in range(random.randint(2, 5))
    ]
)

# Put the buttons array into the table
table = mo.ui.table(
    {
        "Action": ["Action Name"] * len(buttons),
        "Trigger": list(buttons),
    }
)
table
```

3. Get the state value

```python
get_state()
```

### Create a form with multiple UI elements

**Use cases.** Combine multiple UI elements into a form so that submission
of the form sends all its elements to Python.

**Recipe.**

1. Import packages.

```python
import marimo as mo
```

2. Use [`mo.ui.form`](api/inputs/form.md#marimo.ui.form) and
[`Html.batch`](api/html.md#marimo.Html.batch) to create a form with
multiple elements.

```python
form = mo.md(
   r"""
   Choose your algorithm parameters:

   - $\epsilon$: {epsilon}
   - $\delta$: {delta}
   """
).batch(epsilon=mo.ui.slider(0.1, 1, step=0.1), delta=mo.ui.number(1, 10)).form()
form
```

3. Get the submitted form value.

```python
form.value
```

## Working with buttons

### Create a button that triggers computation when clicked

**Use cases.** To trigger a computation on button click and only on button
click, use [`mo.ui.run_button()`](/api/inputs/run_button.md).

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create a run button

```python
button = mo.ui.run_button()
button
```

3. Run something only if the button has been clicked.

```python
mo.stop(not button.value, "Click 'run' to generate a random number")

import random
random.randint(0, 1000)
```

### Create a counter button

**Use cases.** A counter button, i.e. a button that counts the number of times
it has been clicked, is a helpful building block for reacting to button clicks
(see other recipes in this section).

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Use [`mo.ui.button`](api/inputs/button.md#marimo.ui.button) and its
   `on_click` argument to create a counter button.

```python
# Initialize the button value to 0, increment it on every click
button = mo.ui.button(value=0, on_click=lambda count: count + 1)
button
```

3. Get the button value

```python
button.value
```

### Create a toggle button

**Use cases.** Toggle between two states using a button with a button
that toggles between `True` and `False`. (Tip: you can also just use
[`mo.ui.switch`](api/inputs/switch.md#marimo.ui.switch).)

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Use [`mo.ui.button`](api/inputs/button.md#marimo.ui.button) and its
   `on_click` argument to create a toggle button.

```python
# Initialize the button value to False, flip its value on every click.
button = mo.ui.button(value=False, on_click=lambda value: not value)
button
```

3. Toggle between two outputs using the button value.

```python
mo.md("True!") if button.value else mo.md("False!")
```

### Re-run a cell when a button is pressed

**Use cases.** For example, you have a cell showing a random sample of data,
and you want to resample on button press.

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create a button without a value, to function as a _trigger_.

```python
button = mo.ui.button()
button
```

3. Reference the button in another cell.

```python
# the button acts as a trigger: every time it is clicked, this cell is run
button

# Replace with your custom logic
import random
random.randint(0, 100)
```

### Run a cell when a button is pressed, but not before

**Use cases.** Wait for confirmation before executing downstream cells
(similar to a form).

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create a counter button.

```python
button = mo.ui.button(value=0, on_click=lambda count: count + 1)
button
```

3. Only execute when the count is greater than 0.

```python
# Don't run this cell if the button hasn't been clicked, using mo.stop.
# Alternatively, use an if expression.
mo.stop(button.value == 0)

mo.md(f"The button was clicked {button.value} times")
```

### Reveal an output when a button is pressed

**Use cases.** Incrementally reveal a user interface.

**Recipe.**

1. Import packages

```python
import marimo as mo
```

2. Create a counter button.

```python
button = mo.ui.button(value=0, on_click=lambda count: count + 1)
button
```

3. Show an output after the button is clicked.

```python
mo.md("#" + "🍃" * button.value) if button.value > 0 else None
```

## Caching

### Cache function outputs in memory

**Use case.** Because marimo runs cells automatically as code and
UI elements change, it can be helpful to cache expensive intermediate
computations. For example, perhaps your notebook computes t-SNE, UMAP, or PyMDE
embeddings, and exposes their parameters as UI elements. Caching the embeddings
for different configurations of the elements would greatly speed up your notebook.

**Recipe.**

1. Use [`mo.cache`](#marimo.cache) to cache function outputs given inputs.

```python
import marimo as mo

@mo.cache
def compute_predictions(problem_parameters):
   # replace with your own function/parameters
   ...
```

Whenever `compute_predictions` is called with a value of `problem_parameters`
it has not seen, it will compute the predictions and store them in a cache. The
next time it is called with the same parameters, instead of recomputing the
predictions, it will return the previously computed value from the cache.

### Persistent caching for very expensive computations

**Use case.** If you are using marimo to capture very compute intensive
results, you may want to save the state of your computations to disk. Ideally,
if you update your code, then this save should be invalidated. It may also be
advantageous to add UI elements to explore your results, without having to
recompute expensive computations. You can achieve this with
[`mo.persistent_cache`](#marimo.persistent_cache).

**Recipe.**

1. Use `mo.persistent_cache` to cache blocks of code to disk.

```python
import marimo as mo

with mo.persistent_cache("my_cache"):
    # This block of code, and results will be cached to disk
    ...
```

If the execution conditions are the same, then cache will load results from
disk, and populate variable definitions.