Filtering datasets with $where

While we can filter datasets before we import them into Incanter, Incanter makes it easy to filter and create new datasets from the existing ones. We'll take a look at its query language in this recipe.

Getting ready

We'll use the same dependencies, imports, and data as we did in the Selecting columns with $ recipe.

How to do it…

Once we have the data, we query it using the $where function:

1. For example, this creates a dataset with a row for the percentage of China's total land area that is used for agriculture:

   user=> (def land-use
            (i/$where {:Indicator-Code "AG.LND.AGRI.ZS"}
                      chn-data))
   user=> (i/nrow land-use)
   1
   user=> (i/$ [:Indicator-Code :2000] land-use)
   ("AG.LND.AGRI.ZS" "56.2891584865366")

2. The queries can be more complicated too. This expression picks out the data that exists for 1962 by filtering any empty strings in that column:

   user=> (i/$ (range 5) [:Indicator-Code :1962]
            (i/$where {:1962 {:ne ""}} chn-data...