Basics

Getting started

From CSV to Cube

In this part of the tutorial, you will create your first cube from a CSV file and learn multidimensionnal concepts such as cube, dimension, hierarchy, measure.

Let’s start by creating a session:

import atoti as tt

session = tt.create_session()

We can now load the data from a CSV file into an in-memory table called a store:

sales_store = session.read_csv("data/sales.csv", keys=["Sale ID"])

We can have a look at the loaded data. They are sales from a company:

sales_store.head()

	Date	Shop	Product	Quantity	Unit price	Amount
Sale ID
S000000000	2020-06-12	shop_0	TAB_0	1.0	210.0	210.0
S000000001	2020-06-11	shop_1	TAB_1	1.0	300.0	300.0
S000000002	2020-06-10	shop_2	CHA_2	2.0	60.0	120.0
S000000003	2020-06-09	shop_3	BED_3	1.0	150.0	150.0
S000000004	2020-06-08	shop_4	BED_4	3.0	300.0	900.0

We will come back to stores in details later, for now we will use the one we have to build a cube:

cube = session.create_cube(sales_store)

That’s it, you have created your first cube! But what’s a cube exactly and how to use it?

Multidimensional concepts

A cube is a multidimensional view of some data, making it easy to explore, aggregate, filter and compare. It’s called a cube because each attribute of the data can be represented as a dimension of the cube:

The axes of the cube are called hierarchies. The purpose of multidimensionnal analysis is to visualize some numeric indicators at specific coordinates of the cube. These indicators are called measures. An example of measure would be the amount of products sold.

We can list the hierarchies in our cube:

# Aliasing the hierarchies property to a shorter variable name because we will use it a lot.
h = cube.hierarchies
h

• Dimensions
  • Hierarchies
    • Date
      1. Date
    • Product
      1. Product
    • Sale ID
      1. Sale ID
    • Shop
      1. Shop

The cube has automatically created a hierarchy for each non numeric field: “Date”, “Product”, “Sale ID” and “Shop”.

You can see that the hierarchy are grouped into dimensions. Here we have a single dimension, the default one, called “Hierarchies” but we will later group the hierarchies about the same concept in the same dimension.

Hierarchies are also made of levels. Levels of the same hierarchy are attributes with a parent-child relationship. For instance, a city belongs to a country so “Country” and “City” could be the two levels of a “Geography” hierarchy.

At the moment, to keep it simple, we only have single-level hierarchies.

lvl = cube.levels

Let’s have a look at the measures of the cube that have been inferred from the data:

m = cube.measures
m

• Measures
  • Amount.MEAN
    • formatter: DOUBLE[#,###.00]
    • visible: True
  • Amount.SUM
    • formatter: DOUBLE[#,###.00]
    • visible: True
  • Quantity.MEAN
    • formatter: DOUBLE[#,###.00]
    • visible: True
  • Quantity.SUM
    • formatter: DOUBLE[#,###.00]
    • visible: True
  • Unit price.MEAN
    • formatter: DOUBLE[#,###.00]
    • visible: True
  • Unit price.SUM
    • formatter: DOUBLE[#,###.00]
    • visible: True
  • contributors.COUNT
    • formatter: None
    • visible: True

The cube has automatically created the sum and mean aggregations for all the numeric fields of the dataset.

Note that a measure isn’t a single result number, it’s more a formula that can be evaluated for any coordinates of the cube.

For instance, we can see the grand total of “Quantity.SUM”, which means summing the sold quantities over the whole dataset:

cube.query(m["Quantity.SUM"])

	Quantity.SUM
0	8077.0

But we can also dice the cube to get the quantity for each “Shop”, which means taking one slice of the cube for each “Shop”:

cube.query(m["Quantity.SUM"], levels=lvl["Shop"])

	Quantity.SUM
Shop
shop_0	202.0
shop_1	202.0
shop_10	203.0
shop_11	203.0
shop_12	201.0
shop_13	202.0
shop_14	202.0
shop_15	202.0
shop_16	201.0
shop_17	204.0
shop_18	202.0
shop_19	202.0
shop_2	202.0
shop_20	201.0
shop_21	201.0
shop_22	201.0
shop_23	203.0
shop_24	203.0
shop_25	201.0
shop_26	202.0
shop_27	202.0
shop_28	202.0
shop_29	201.0
shop_3	201.0
shop_30	204.0
shop_31	202.0
shop_32	202.0
shop_33	201.0
shop_34	201.0
shop_35	201.0
shop_36	203.0
shop_37	203.0
shop_38	201.0
shop_39	202.0
shop_4	204.0
shop_5	202.0
shop_6	202.0
shop_7	201.0
shop_8	201.0
shop_9	201.0

We can slice on a single “Shop”:

cube.query(
    m["Quantity.SUM"], condition=lvl["Shop"] == "shop_0",
)

	Quantity.SUM
0	202.0

We can dice along 2 different axes and take the quantity per product and date.

cube.query(m["Quantity.SUM"], levels=[lvl["Date"], lvl["Product"]])

		Quantity.SUM
Date	Product
2020-05-14	BED_24	8.0
	BED_25	4.0
	BED_26	6.0
	BED_27	4.0
	BED_3	2.0
...	...	...
2020-06-12	TSH_52	6.0
	TSH_53	4.0
	TSH_7	3.0
	TSH_8	5.0
	TSH_9	3.0

1830 rows × 1 columns

We can even combine these operations to slice on one hierarchy and dice on the two others:

cube.query(
    m["Quantity.SUM"],
    levels=[lvl["Date"], lvl["Product"]],
    condition=lvl["Shop"] == "shop_0",
)

		Quantity.SUM
Date	Product
2020-05-23	BED_24	1.0
	BED_26	1.0
	BED_3	1.0
	BED_4	1.0
	BED_46	1.0
...	...	...
2020-06-12	TSH_51	2.0
	TSH_52	1.0
	TSH_53	1.0
	TSH_7	1.0
	TSH_9	1.0

125 rows × 1 columns

First visualization

So far we have used cube.query which returns a table as a pandas DataFrame but a better way to visualize multidimensional data is a pivot table. With atoti’s JupyterLab extension, you can do advanced and interactive visualizations such as pivot tables and charts directly into your notebook by calling cube.visualize().

This will create a widget and open the atoti tab on the left with tools to manipulate the widget.

Let’s start by creating a pivot table:

• Run cube.visualize().

• Select “Pivot table”.

• In the left panel, click on a measure such as “Amount.SUM” to add it.

• Click on a hierarchy such as “Date” to get the Amount per date.

• Drag and drop another hierarchy such as “Product” to the “Columns” section to get the amount sold per day and per product.

cube.visualize()

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We can also create a first chart representing the evolution of the amount sold per day:

• Run cube.visualize().

• Select “Chart”.

• Click on the “Amount.SUM” measure to add it to the chart.

• Click on the “Date” hierachy to add it to the chart.

cube.visualize()

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Drilldown and filters

Multidimensional analysis is meant to be done from top to bottom: start by visualizing the indicators at the top level then drilldown to explain the top figures with more details.

For instance, we can visualize some measures per date then drilldown on the “Shops” for a specific date, then see the products sold by a specific “Shop” on this date.

Using the previous cube representation, this is like zooming more and more on a part of the cube.

cube.visualize()

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It’s also very easy to filter on a hierarchy when building widgets. Let’s apply a filter on a chart:

cube.visualize()

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Dashboarding application

Being able to quickly build widgets inside a notebook without coding is nice to rapidly explore the data, iterate on your model and share some results. However, to provide richer insights, dashboards are even better. That’s why atoti comes with a web application that can be accessed outside of the notebook and where widgets can be laid out to form dashboards.

The URL of this application can be accessed like that:

session.url

'http://localhost:42767'

It’s possible to publish widgets built in the notebook to the application by right clicking on them and selecting “Publish widget in app”. They will then be available in the “Saved widgets” section.

Enriching the cube

In the previous section, you have learned how to create a basic cube and manipulate it. We will now enrich this cube with additional attributes and more interesting measures.

Join

Currently, we have very limited information about our products: only the ID. We can load a CSV containing more details into a new store:

products_store = session.read_csv("data/products.csv", keys=["Product"])

Note that a store can have a set of keys. These keys are the columns which make each line unique. Here, it’s the product ID.

If you try to insert a new row with the same keys as an existing row, it will override the existing one.

products_store.head()

	Category	Sub category	Size	Purchase price	Color	Brand
Product
TAB_0	Furniture	Table	1m80	190.0	black	Basic
TAB_1	Furniture	Table	2m40	280.0	white	Mega
CHA_2	Furniture	Chair	N/A	48.0	blue	Basic
BED_3	Furniture	Bed	Single	127.0	red	Mega
BED_4	Furniture	Bed	Double	252.0	brown	Basic

This store contains the category, subcategory, size, color, purchase price and brand of the product. Both stores have a “Product” field we can use to join them.

Note that this is a database-like join and not a pandas-like join. All the details from products_store won’t be inlined into sales_store. Instead, this just declares a reference between these two stores that the cube can use to provide more analytical axes.

sales_store.join(products_store, mapping={"Product": "Product"})

You can visualize the structure of the whole datastore:

session.stores.schema

The new columns have been automatically added to the cube as hierarchies:

h

• Dimensions
  • Hierarchies
    • Brand
      1. Brand
    • Category
      1. Category
    • Color
      1. Color
    • Date
      1. Date
    • Product
      1. Product
    • Sale ID
      1. Sale ID
    • Shop
      1. Shop
    • Size
      1. Size
    • Sub category
      1. Sub category

You can use them directly in a new widget. For instance, let’s create a bar chart to visualize the mean price per subcategory of product:

cube.visualize()

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We can also make a donut chart to see how all the sales are distributed between brands:

cube.visualize()

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In a similar way, we can enrich the data about the “Shops”:

shops_store = session.read_csv("data/shops.csv", keys=["Shop ID"])
shops_store.head()

	City	State or region	Country	Shop size
Shop ID
shop_0	New York	New York	USA	big
shop_1	Los Angeles	California	USA	medium
shop_2	San Diego	California	USA	medium
shop_3	San Jose	California	USA	medium
shop_4	San Francisco	California	USA	small

sales_store.join(shops_store, mapping={"Shop": "Shop ID"})
session.stores.schema

We can now plot the evolution of the sales per country over time:

cube.visualize()

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New measures

So far we have only used the default measures which are basic aggregations of the numeric columns. We can add new custom measures to our cube.

Max

We’ll start with a simple aggregation taking the maximum price of the sales store:

m["Max price"] = tt.agg.max(sales_store["Unit price"])

This new measure is directly available:

cube.query(m["Max price"])

	Max price
0	440.0

cube.query(m["Max price"], levels=lvl["Category"])

	Max price
Category
Cloth	60.0
Furniture	440.0

Margin

Now that the price of each product is available from the products store, we can compute the margin.

To do that, we start by computing the cost which is the quantity sold multiplied by the purchase price, summed over all the products.

Note the use of the origin scope instructing to perform the multiplication for each product and then do the sum.

cost = tt.agg.sum(
    m["Quantity.SUM"] * products_store["Purchase price"],
    scope=tt.scope.origin(lvl["Product"]),
)

m["Margin"] = m["Amount.SUM"] - cost

We can also define the margin rate which is the ratio of the margin by the the sold amount:

m["Margin rate"] = m["Margin"] / m["Amount.SUM"]

cube.query(m["Margin"], m["Margin rate"], levels=lvl["Product"])

	Margin	Margin rate
Product
BED_24	3082.0	0.153333
BED_25	6336.0	0.160000
BED_26	8060.0	0.156962
BED_27	8580.0	0.147727
BED_3	3036.0	0.153333
...	...	...
TSH_52	520.0	0.166667
TSH_53	396.0	0.125000
TSH_7	393.0	0.150000
TSH_8	264.0	0.100000
TSH_9	390.0	0.136364

61 rows × 2 columns

Let’s use this margin rate to do a “Top 10” filter to see the products with the best rate.

Note that you don’t need to put the rate measure and the product level in the pivot table to apply the filter.

cube.visualize("10 most profitable products")

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Cumulative sum over time

A cumulative sum is the partial sum of the data up to the current value. For instance, a cumulative sum over time can be used to show how some measure changes over time.

m["Cumulative amount"] = tt.agg.sum(
    m["Amount.SUM"], scope=tt.scope.cumulative(lvl["Date"])
)

cube.visualize()

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Average per store

Aggregations can also be combined. For instance, we can sum inside a “Shop”: then take the average of this to see how much a store sales on average:

m["Average amount per shop"] = tt.agg.mean(
    m["Amount.SUM"], scope=tt.scope.origin(lvl["Shop"])
)

cube.query(m["Average amount per shop"])

	Average amount per shop
0	24036.575

cube.query(m["Average amount per shop"], levels=lvl["Sub category"])

	Average amount per shop
Sub category
Bed	12728.875
Chair	601.500
Hoodie	1403.200
Shoes	3184.500
Table	5023.500
Tshirt	1095.000

Fact-level operations

sales_store.head()

	Date	Shop	Product	Quantity	Unit price	Amount
Sale ID
S000000019	2020-05-24	shop_19	SHO_19	2.0	60.0	120.0
S000000036	2020-06-06	shop_36	SHO_36	1.0	60.0	60.0
S000000061	2020-06-11	shop_21	TAB_0	1.0	210.0	210.0
S000000110	2020-05-23	shop_30	TSH_49	2.0	20.0	40.0
S000000130	2020-06-02	shop_10	TSH_8	1.0	20.0	20.0

As you can see, our data already contains an “Amount” column which is equal to “Quantity” * “Unit price”. It’s a good practice to do this kind of fact-level preprocessing outside atoti. Indeed, it avoids redoing these computations on every row over and over, slowing down every query. Like that, atoti only has to do what it’s the best at: aggregation.

Multilevel hierarchies

So far, all our hierarchies only had one level but it’s best to regroup attributes with a parent-child relationship in the same hierarchy.

For example, we can group the “Category”, “SubCategory” and “Product ID” levels into a “Product” hierarchy:

h["Product"] = [lvl["Category"], lvl["Sub category"], lvl["Product"]]

And let’s remove the old hierarchies:

del h["Category"]
del h["Sub category"]

h

• Dimensions
  • Hierarchies
    • Brand
      1. Brand
    • City
      1. City
    • Color
      1. Color
    • Country
      1. Country
    • Date
      1. Date
    • Product
      1. Category
      2. Sub category
      3. Product
    • Sale ID
      1. Sale ID
    • Shop
      1. Shop
    • Shop size
      1. Shop size
    • Size
      1. Size
    • State or region
      1. State or region

We can also do it with “City”, “Region” and “Country” to build a “Geography” hierarchy.

Note that instead of using existing levels you can also define a hierarchy with the fields of the store the levels will be based on:

h["Geography"] = [
    shops_store["Country"],
    shops_store["State or region"],
    shops_store["City"],
]
del h["Country"]
del h["State or region"]
del h["City"]

As we are restructuring the hierarchies, let’s use this opportunity to also change the dimensions.

A dimension regroups hierarchies of the same concept.

To keep it simple here, we will simply move the new “Geography” hierarchy to its own dimension:

h["Geography"].dimension = "Location"
h

• Dimensions
  • Hierarchies
    • Brand
      1. Brand
    • Color
      1. Color
    • Date
      1. Date
    • Product
      1. Category
      2. Sub category
      3. Product
    • Sale ID
      1. Sale ID
    • Shop
      1. Shop
    • Shop size
      1. Shop size
    • Size
      1. Size
  • Location
    • Geography
      1. Country
      2. State or region
      3. City

With that, we can define new measures taking advantage of the multilevel structure. For instance, we can create a measure indicating how much a product contributes to its subcategory:

m["Parent category amount"] = tt.parent_value(m["Amount.SUM"], on=h["Product"])

m["Percent of parent amount"] = m["Amount.SUM"] / m["Parent category amount"]

cube.visualize()

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Polishing the cube

Deleting or hiding measures

Some measures have been automatically created from numeric fields but are not useful. For instance, “Unit Price.SUM” does not really make sense as we never want to sum the unit prices. We can delete it:

del m["Unit price.SUM"]

Other measures have been used while building the project only as intermediary steps but are not useful to the end users in the application. We can hide them from the UI (they will remain accessible in Python):

m["Parent category amount"].visible = False

Measure folders

Measures can be rearranged into folders.

for measure in [
    m["Amount.MEAN"],
    m["Amount.SUM"],
    m["Average amount per shop"],
    m["Cumulative amount"],
    m["Percent of parent amount"],
]:
    measure.folder = "Amount"

Measure formatters

Some measures can be formatted for a nicer display. Classic examples of this is changing the number of decimals or adding a percent or a currency symbol.

Let’s do this for our percent of parent amount and margin rate:

Before

m["Percent of parent amount"].formatter = "DOUBLE[0.00%]"
m["Margin rate"].formatter = "DOUBLE[0.00%]"

After

Simulations

Simulations are a way to compare several scenarios and do what-if analysis. This is very powerful as it helps understanding how changing the source data or a piece of the model impact the key indicators.

In atoti, the data model is made of measures chained together. A simulation can be seen as changing one part of the model, either its source data or one of its measure definitions, and then evaluating how it impacts the following measures.

Source simulation

Let’s start by changing the source. With pandas or Spark, if you want to compare two results for a different versions of the entry dataset you have to reapply all the transformations to your dataset. With atoti, you only have to provide the new data and all the measures will be automatically available for both versions of the data.

We will create a new scenario using pandas to modify the original dataset.

import pandas as pd

For instance, we can simulate what would happen if we had managed to purchase some products at a cheaper price.

products_df = pd.read_csv("data/products.csv")
products_df.head()

	Product	Category	Sub category	Size	Purchase price	Color	Brand
0	TAB_0	Furniture	Table	1m80	190.0	black	Basic
1	TAB_1	Furniture	Table	2m40	280.0	white	Mega
2	CHA_2	Furniture	Chair	NaN	48.0	blue	Basic
3	BED_3	Furniture	Bed	Single	127.0	red	Mega
4	BED_4	Furniture	Bed	Double	252.0	brown	Basic

better_prices = {
    "TAB_0": 180.0,
    "TAB_1": 250.0,
    "CHA_2": 40.0,
    "BED_3": 110.0,
    "BED_4": 210.0,
}

for product, purchase_price in better_prices.items():
    products_df.loc[
        products_df["Product"] == product, "Purchase price"
    ] = purchase_price
products_df.head()

	Product	Category	Sub category	Size	Purchase price	Color	Brand
0	TAB_0	Furniture	Table	1m80	180.0	black	Basic
1	TAB_1	Furniture	Table	2m40	250.0	white	Mega
2	CHA_2	Furniture	Chair	NaN	40.0	blue	Basic
3	BED_3	Furniture	Bed	Single	110.0	red	Mega
4	BED_4	Furniture	Bed	Double	210.0	brown	Basic

We can now load this new dataframe into a new scenarios of the product store.

products_store.scenarios["Cheaper purchase prices"].load_pandas(products_df)

Using the “Source Simulation” hierarchy we can display the margin of the scenario and compare it to the base case.

cube.visualize()

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Note that all the existing measures are immediately available on the new data. For instance, the margin rate still exists, and we can see that in this scenario we would have a better margin for the Furniture products.

cube.visualize()

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Measures simulations

The other simulation technique is to change the value of a measure for some coordinates. The value of the simulated measure can be multiplied by some factor, added to a fixed amount, or completely replaced.

When creating the simulation, you can choose at which granularity the modification applies. For instance, we can create a simulation of the quantity and amount measures per country. Doing that, we can answer questions such as “What happens if there is a crisis in France and we sell 20% less ?”

quantity_simu = cube.setup_simulation(
    "Country Simulation",
    levels=[lvl["Country"]],
    multiply=[m["Quantity.SUM"], m["Amount.SUM"]],
)

Let’s add a first scenario to this simulation:

france_crisis = quantity_simu.scenarios["France crisis"]

A scenario is like a store where you can add new parameters to configure the scenario. In this scenario, we decided that France sell 20% less so let’s multiply the quantity and the amount by 80% only for France.

france_crisis += ("France", 0.80, 0.80)
france_crisis.head()

	Country Simulation_Quantity.SUM_multiply	Country Simulation_Amount.SUM_multiply	Priority
Country
France	0.8	0.8	0.0

Let’s query the cube using the new “Country Simulation” hierarchy to compare the quantity and amount between the base case and our new scenario:

cube.query(
    m["Quantity.SUM"],
    m["Amount.SUM"],
    levels=[lvl["Country Simulation"], lvl["Country"]],
)

		Quantity.SUM	Amount.SUM
Country Simulation	Country
Base	France	3027.0	358042.0
	USA	5050.0	603421.0
France crisis	France	2421.6	286433.6
	USA	5050.0	603421.0

Note that you are not limited to a single scenario:

quantity_simu.scenarios["US boost"] += ("USA", 1.15, 1.15)

cube.query(m["Quantity.SUM"], levels=[lvl["Country Simulation"], lvl["Country"]])

		Quantity.SUM
Country Simulation	Country
Base	France	3027.0
	USA	5050.0
France crisis	France	2421.6
	USA	5050.0
US boost	France	3027.0
	USA	5807.5

As the amount has been modified, the measures depending on it such as the cumulative amount are also impacted.

cube.visualize()

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Finally, we can even combine the different simulations (the source one and the measure one) to create a matrix of scenarios:

cube.visualize()

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Summary

In this tutorial, you have learned all the basics to build a project with atoti, from the concept of multidimensional to powerful simulations. We now encourage you to try the library with your own data!