How to create Typescript map?

Question

I would like to create a Map total which can be used like: total['cashBalance'].sum

based on existing data

const fields = ['cashBalance', 'openTradeEquity', 'initialMargin', 'optionValue', 'treasuries', 'margin'];

I am trying as below but it is not working.

const total: Map<string, {sum: number}> = fields.map(f => [f, {sum: 0}]) ;

Surely, I am not getting the syntax right... can anyone please help me with this? Thanks Anand

Did you mean "but it is not working"? Also, instead of saying "it's not working", it would be more helpful to give an error message, or the result you got instead of what you expected. — kingdaro
– kingdaro, Commented Apr 6, 2018 at 13:07

kingdaro · Accepted Answer · 2018-04-06 14:15:13Z

3

The array's map function creates a new array from an existing one, and doesn't create a map. Here, you want to use the Map object instead. Loop through all of the items in fields and add an item to the map for each one.

const total = new Map<string, { sum: number }>()
for (const field of fields) {
  total.set(field, { sum: 0 })
}

total.get('cashBalance').sum // 0

edited Apr 6, 2018 at 14:15

answered Apr 6, 2018 at 13:10

kingdaro

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3 Comments

ComFreek Over a year ago

Shorter: const total: Map<string, { sum: number }> = new Map(fields.map(f => [f, { sum: 0 }] as [string, { sum: number }]));. Unfortunately the type cast is necessary.

kingdaro Over a year ago

I'd rather go with the readable approach over the shorter one

Anand Over a year ago

Thank you so much @kingdaro

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