Tidy data - a revisit

It would be useful to add the Distribution variable from NESP_SharkSpeciesList to QldShark_2017_Clean_v2, but the data in that column is very messy with multiple values inside the cells. Do a Text facet on the Distribution column and explore.

To create a tidy dataset, where:

Each variable forms a column
Each observation forms a row
Each cell has one value
Each type of observational unit forms a table,

multi-value cells need to be split by the value.

This task is helpful where there are multiple values in a cell that are not organised consistently, such as when survey respondents can select multiple, controlled values to answer a question, or a notes field has free text. The Distribution column is an example of this. Let’s add the column to QldShark_2017_Clean_v2 then tidy it.

Add a new column

Go to QldShark_2017_Clean_v2
Select Common name column Edit Column > Add column based on this column
name the new Column Distribution
enter this GREL expression:

cell.cross("NESP_SharkSpeciesList","Common name")[0].cells["Distribution"].value

382 rows of the shark captures now have a new variable & value of Distribution added.

Now we need to tidy the new variable in QldShark_2017_Clean_v2, then split the column into two columns with a value in each.

Split a multi-value column

Go to QldShark_2017_Clean_v2
Select column Distribution > Facet > Text Facet
There are 6 choices. Two of the choices contain two values within the cells e.g. Australasia & Indonesia. The multiple values do not contain a common separator. This will need fixing to be able to split on.

Let’s change the blank choice to “NULL” as these records do not have any data.

In Distribution Facet box hover over (blank)
Select edit and type NULL > Apply
At Distribution column
Select Edit cells > Replace > Find: & Replace with: ;
Select Edit column > Split in several columns > by separator *;* > Split into *2* columns
ok.

An additional Distribution column will be created with values only appearing where there had previously been two values in the original cell.

Watch these steps in this video.

Now let’s explore the column Notes on skies and wind. It is messy and contains multiple values within the cells. Ultimately we will create multiple columns using GREL and a language known as Regular Expression or Regex, which searches for patterns in strings.

Add new columns using GREL & Regex

Go to column Notes on skies and wind
Select Facet > Text facet and explore the 36 choices

Notice the variations in common separators, order of values and case format. We cannot split the variable into multiple columns using the method.

Hover over the (blank) choice select edit and change (blank) to NULL
Select Edit cells > Common transforms > to lower case to make the case consistent throughout the cell (and reduce the choices to 31)
Select Edit column> add column based on this column
Type new column name Overcast
Click inside expression box, enter GREL expression:

if(value.contains("overcast"),"overcast",value).replace(/.*[^overcast].*/,"")

This means… if (the value in the cell contains “overcast”, replace it with “overcast” value), then replace (anything that is not “overcast” that is found one or more times in the cell, with “” ie. a blank).
Preview and ok
Repeat steps above for the other Sky related value fine (can reuse expression from history tab)

Now let’s join up the two columns fine and overcast which are really values, into a new variable Skies

Go to fine column Edit column > Join columns...
Select fine and overcast from tick box list
Select Write result in new column named...
Type Skies and ok.

We now have a new variable Skies. Perform and text facet to see the value choices.

Hover over (blank) choice select edit and type NULL and Apply. Now each cell has data.

Next we can extract all the “wind” data into a new variable using the steps above.

Select Edit column> add column based on this column
Type new column name strong breeze
Click inside expression box, enter GREL expression:

if(value.contains("strong breeze"),"strong breeze",value).replace(/.*[^strong breeze].*/,"")
Preview and ok
Repeat steps above for the other “wind” related values that can be found in the Text facet window near gale and light winds (can reuse expression from history tab).

Now let’s join up the 3 columns strong breeze, near gale, light winds which are really values, into a new variable Wind

Go to near gale column Edit column > Join columns...
Select strong gale, calm winds, strong breeze, near gale, light winds, gale force, light breeze from tick box list
Select Write result in new column named...
Type Wind and ok.

We now have a new variable Wind. Perform a text facet to see the value choices.

Hover over (blank) choice select edit and type NULL and Apply. Now each cell has data.
Go to All column Edit columns > Re-order / remove columns...
Drag and drop the following columns to remove: fine, overcast, Notes on skies and wind , near gale , strong breeze, light winds
ok.

This great GREL cheat sheet from code4lib Toronto has more details on building expressions using Regex.

See how this works in the video below.

The final step is to export specific variables from this tidy dataset to a .csv file which can be parsed (understood by) the geo.json tool used in the next lesson.

Export selected columns to .csv file

Go to All column >Edit Columns> Reorder Remove columns
Drag and drop the columns not needed including Species Code, Date, Area, Location, ` Genus, Species, Distribution, Distribution1, to the remove` box.
Common name, Latitude, Longitude, Length (m), Rainfall_mm, Formatted Date, Water Temp (C), Skies, Wind will remain
Ok
Click Export button, top right hand corner
Select Comma-separated value dataset
save file

<-- BACK | NEXT -->