Tutorial by Topics: eval



To build a dynamic and interactive PHP program, it is useful to output variables and their values. The PHP language allows for multiple methods of value output. This topic covers the standard methods of printing a value in PHP and where these methods can be used.

In JavaScript, the eval function evaluates a string as if it were JavaScript code. The return value is the result of the evaluated string, e.g. eval('2 + 2') returns 4.

eval is available in the global scope. The lexical scope of the evaluation is the local scope unless invoked indirectly (e.g. var geval = eval; geval(s);).

The use of eval is strongly discouraged. See the Remarks section for details.

At certain points, you will be evaluating a range of data and you will need to locate the duplicates in it. For bigger data sets, there are a number of approaches you can take that use either VBA code or conditional functions. This example uses a simple if-then condition within two nested for-next loops to test whether each cell in the range is equal in value to any other cell in the range.

You can use hierarchical queries to retrieve data based on a natural hierarchical relationship between rows in a table

Dplyr and many modern libraries in R use non-standard evaluation (NSE) for interactive programming and standard evaluation (SE) for programming1.

For instance, the summarise() function use non-standard evaluation but relies on the summarise_() which uses standard evaluation.

The lazyeval library makes it easy to turn standard evaluation function into NSE functions.


Page 1 of 2