![]() You could use this behavior – and nothing else – to create a reactive web app. In other words, R will not execute an expression until you force it to. However, you must tell R to run the expresssion for this to happen because R uses a style of execution known as lazy evaluation. It looks up the current value of each object that it uses and computes new ouput. Think of it like this: every time you run an expression, the expression updates itself. a <- 1 print ( a ) # 1 a <- 2 print ( a ) # 2 This isn’t reactivity it’s just standard R behavior. ![]() Everything in R updates itself each time it is run. Updating an out of date expression is not hard: you just need to re-run the expression. For example, at the end of this code, the expression print(a) is out of date. Reactivity ensures that the output of print(input$a) is always up to date, but what does it mean for output to be out of date? Let’s consider output – and the expression that made it – to be out of date if one of the objects in the expression has been given a new value since the expression was called. #Update r studio update#R expressions update themselves, if you ask
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