Sum table column conditionally

App Building
1
  • Goal: Hi guys, I have a table with names and prices in it. I want to sum the prices column but depending on the name column, basically like this:

A - 500
B - 300
C - 400
B - 900
G - 100
C - 300

Now I want to do something like "Give me the sum of everything with the name B", so the result should be 1200

I can sum up a column like this: _.sum(table1.data.map(i=>parseFloat(i.price)))

But how can I built in the additional condition?

2

The nature of the map function is that it will return a value for every item in your array. So you can approach this in (at least) two ways.

  1. filter the initial array with your condition and then only map for the prices over the result:
_.sum(table1.data.filter(i=>i.name === yourConditionalValue).map(i=>parseFloat(i.price)))
  1. return 0 in the mapping function when your condition is not met:
_.sum(table1.data.map(i => { 
if(i.name === yourConditionalValue) return parseFloat(i.price)
else return 0
}))

I think #1 is a bit more logical to follow for readability.