count_equal: determine number of field elements equal to a given value

count_equal(grid, field, value)[source]

Sum the number of array elements equal to a value.

count_equal calculates number of values in the core nodes of the model grid that are equal to the input value.

Parameters

  • grid (Landlab model grid) –

  • field (str) – An at-node Landlab grid field that is present on the model grid.

  • value (float) – The value to identify within the field.

Returns

out – The number of elements in the field array equal to value.

Return type

float

Examples

First an example that only uses the count_equal function.

>>> from landlab import RasterModelGrid
>>> from landlab.components import FlowAccumulator
>>> from umami.calculations import count_equal
>>> grid = RasterModelGrid((10, 10))
>>> z = grid.add_zeros("node", "topographic__elevation")
>>> z += grid.x_of_node + grid.y_of_node
>>> fa = FlowAccumulator(grid)
>>> fa.run_one_step()
>>> count_equal(grid, "topographic__elevation", 4)
3
>>> count_equal(grid, "drainage_area", 1)
8

Next, the same calculations are shown as part of an umami Metric.

>>> from io import StringIO
>>> from umami import Metric
>>> file_like=StringIO('''
... elev4:
...     _func: count_equal
...     field: topographic__elevation
...     value: 4
... num_headwater_nodes:
...     _func: count_equal
...     field: drainage_area
...     value: 1
... ''')
>>> metric = Metric(grid)
>>> metric.add_from_file(file_like)
>>> metric.names
['elev4', 'num_headwater_nodes']
>>> metric.calculate()
>>> metric.values
[3, 8]