Nina Zumel had a really great article on how to prepare a nice Keras performance plot using R.

I will use this example to show some of the advantages of cdata record transform specifications.

The model performance data from Keras is in the following format:

# R code

library(wrapr)

df <- wrapr::build_frame(
  "val_loss"  , "val_acc", "loss" , "acc" , "epoch" |
    -0.377    , 0.8722   , -0.5067, 0.7852, 1       |
    -0.2997   , 0.8895   , -0.3002, 0.904 , 2       |
    -0.2964   , 0.8822   , -0.2166, 0.9303, 3       |
    -0.2779   , 0.8899   , -0.1739, 0.9428, 4       |
    -0.2843   , 0.8861   , -0.1411, 0.9545, 5       |
    -0.312    , 0.8817   , -0.1136, 0.9656, 6       )

knitr::kable(df[1, , drop = FALSE])

And the form that would be easiest to use with ggplot2 would be the following:

# R code

pf <- wrapr::build_frame(
 "epoch" , "measure" , "training", "validation" |
 1 , "minus binary cross entropy", -0.5067 , -0.377 |
 1 , "accuracy" , 0.7852 , 0.8722 )

knitr::kable(pf)

In her article Nina Zumel shows a cdata transform solution which we re-interpret as the following:

# R code

library(cdata)

# define the record shape we want by example
controlTable <- wrapr::qchar_frame(
  "measure"                     , "training", "validation" |
    "minus binary cross entropy", loss      , val_loss     |
    "accuracy"                  , acc       , val_acc      )

# use our example record shape to specify the record transform
transform <- rowrecs_to_blocks_spec(
  controlTable = controlTable,
  recordKeys = 'epoch')

df %.>% transform

##    epoch                    measure training validation
## 1      1 minus binary cross entropy  -0.5067    -0.3770
## 2      1                   accuracy   0.7852     0.8722
## 3      2 minus binary cross entropy  -0.3002    -0.2997
## 4      2                   accuracy   0.9040     0.8895
## 5      3 minus binary cross entropy  -0.2166    -0.2964
## 6      3                   accuracy   0.9303     0.8822
## 7      4 minus binary cross entropy  -0.1739    -0.2779
## 8      4                   accuracy   0.9428     0.8899
## 9      5 minus binary cross entropy  -0.1411    -0.2843
## 10     5                   accuracy   0.9545     0.8861
## 11     6 minus binary cross entropy  -0.1136    -0.3120
## 12     6                   accuracy   0.9656     0.8817

We have a tutorial on how to design such transforms by writing down the shape your incoming data records are arranged in, and also the shape you wish your outgoing data records to be arranged in.

This simple data transform is in fact not a single pivot/un-pivot, as the result records spread data-values over multiple rows and multiple columns at the same time. We call the transform simple, because from a user point of view: it takes records of one form to another form (with the details left to the implementation).

In this note I would like to comment on some of the great advantages of using a data driven record transform specification.

First, as we see above and in the tutorial, once learned the specification system is very easy (and powerful).

Next: we can print the transformation and check if it matches our intent:

# R code

print(transform)

## {
##  row_record <- wrapr::qchar_frame(
##    "epoch"  , "loss", "acc", "val_loss", "val_acc" |
##      .      , loss  , acc  , val_loss  , val_acc   )
##  row_keys <- c('epoch')
## 
##  # becomes
## 
##  block_record <- wrapr::qchar_frame(
##    "epoch"  , "measure"                   , "training", "validation" |
##      .      , "minus binary cross entropy", loss      , val_loss     |
##      .      , "accuracy"                  , acc       , val_acc      )
##  block_keys <- c('epoch', 'measure')
## 
##  # args: c(checkNames = TRUE, checkKeys = FALSE, strict = FALSE, allow_rqdatatable = TRUE)
## }

The important point is that the transform is specified in data (not code):

# R code

str(transform)

## List of 7
##  $ controlTable     :'data.frame':   2 obs. of  3 variables:
##   ..$ measure   : chr [1:2] "minus binary cross entropy" "accuracy"
##   ..$ training  : chr [1:2] "loss" "acc"
##   ..$ validation: chr [1:2] "val_loss" "val_acc"
##  $ recordKeys       : chr "epoch"
##  $ controlTableKeys : chr "measure"
##  $ checkNames       : logi TRUE
##  $ checkKeys        : logi FALSE
##  $ strict           : logi FALSE
##  $ allow_rqdatatable: logi TRUE
##  - attr(*, "class")= chr "rowrecs_to_blocks_spec"

Because the transform is data (not code), it is easy to share with other systems: such as SQL or Python/Pandas.

To show this we will first convert the transform specification into YAML for transport.

# R code

library(yaml)

yaml_str <- transform %.>%
  convert_cdata_spec_to_yaml(.) %.>%
  yaml::as.yaml(.)

cat(yaml_str)

## blocks_out:
##   record_keys: epoch
##   control_table_keys: measure
##   control_table:
##     measure:
##     - minus binary cross entropy
##     - accuracy
##     training:
##     - loss
##     - acc
##     validation:
##     - val_loss
##     - val_acc

We can then import this structure into Python.

# R code

library(reticulate)
use_condaenv("aiAcademy")  # our Python environment, yours will be different

The transported operator can then be used in Python.

# Python code

import yaml
import pandas
import data_algebra
from data_algebra.cdata_impl import record_map_from_simple_obj

record_map = record_map_from_simple_obj(yaml.safe_load(r.yaml_str))

print(record_map)

## Transform row records of the form:
##   record_keys: ['epoch']
##  ['epoch', 'loss', 'acc', 'val_loss', 'val_acc']
## to block records of structure:
## RecordSpecification
##    record_keys: ['epoch']
##    control_table_keys: ['measure']
##    control_table:
##                          measure training validation
##    0  minus binary cross entropy     loss   val_loss
##    1                    accuracy      acc    val_acc

# Python code

print(r.df)

##    val_loss  val_acc    loss     acc  epoch
## 0   -0.3770   0.8722 -0.5067  0.7852    1.0
## 1   -0.2997   0.8895 -0.3002  0.9040    2.0
## 2   -0.2964   0.8822 -0.2166  0.9303    3.0
## 3   -0.2779   0.8899 -0.1739  0.9428    4.0
## 4   -0.2843   0.8861 -0.1411  0.9545    5.0
## 5   -0.3120   0.8817 -0.1136  0.9656    6.0

# Python code

res = record_map.transform(r.df)

print(res)

##     epoch                     measure  training  validation
## 0     1.0                    accuracy    0.7852      0.8722
## 1     1.0  minus binary cross entropy   -0.5067     -0.3770
## 2     2.0                    accuracy    0.9040      0.8895
## 3     2.0  minus binary cross entropy   -0.3002     -0.2997
## 4     3.0                    accuracy    0.9303      0.8822
## 5     3.0  minus binary cross entropy   -0.2166     -0.2964
## 6     4.0                    accuracy    0.9428      0.8899
## 7     4.0  minus binary cross entropy   -0.1739     -0.2779
## 8     5.0                    accuracy    0.9545      0.8861
## 9     5.0  minus binary cross entropy   -0.1411     -0.2843
## 10    6.0                    accuracy    0.9656      0.8817
## 11    6.0  minus binary cross entropy   -0.1136     -0.3120

We can even convert the transform to SQL (either in R directly or in Python directly).

# Python code

from data_algebra.SQLite import SQLiteModel
from data_algebra.data_ops import *

db_model = SQLiteModel()
ops = TableDescription(
    'keras_frame', 
    ["val_loss", "val_acc", "loss", "acc", "epoch"]). \
  convert_records(record_map)

sql_str = ops.to_sql(db_model, pretty=True)
print(sql_str)

## SELECT a."epoch" AS "epoch",
##        b."measure" AS "measure",
##        CASE
##            WHEN b."training" = 'loss' THEN a."loss"
##            WHEN b."training" = 'acc' THEN a."acc"
##            ELSE NULL
##        END AS "training",
##        CASE
##            WHEN b."validation" = 'val_loss' THEN a."val_loss"
##            WHEN b."validation" = 'val_acc' THEN a."val_acc"
##            ELSE NULL
##        END AS "validation"
## FROM ("keras_frame") a
## CROSS JOIN ("cdata_temp_record") b
## ORDER BY a."epoch",
##          b."measure"

The SQL code was generated from the transform specification. This was easy to implement as it is often simple to convert data to code (though it can be quite hard to translate code to data).

And that is some of the power of using data to specify your data transforms.

More on cross-language data processing can be found here, here, and here.