Data Array Undefined React Native

Question

I am trying to map the data I get back from an API in this format:

data={[
    { x: 0, y: 0 },
    { x: 1, y: 1 },
    { x: 2, y: 2 },
    { x: 3, y: 3 },
    { x: 4, y: 4 },
  ]}

I have a get call then I map each of the items to give me an x , y value:

getCryptoChartData('histohour', selectedCrypto, 24, 1).then(
          cryptoChartData => {
            //const response = cryptoChartData.Data.map(item => item.close);
            const data = cryptoChartData.Data.map(item => {
              [
                {
                  x: item.time,
                  y: item.close,
                },
              ];
            });
            return this.setState({cryptoChartData: data});
          },
        );

However, I notice that the data array is set to undefined:

<SlideAreaChart
 data={this.state.cryptoChartData}
/>

Am I setting the data array correctly with the mapping?

Narek Ghazaryan · Accepted Answer · 2021-12-17 22:43:04Z

1

Yes, it seems the problem is in mapping. You just forget to return the generated object:

    const data = cryptoChartData.Data.map(item => {
      return {
          x: item.time,
          y: item.close,
      };
    });

or

const data = cryptoChartData.Data.map(item => ({
    x: item.time,
    y: item.close,
}));

Final code of getCryptoChartData method will look like:

getCryptoChartData('histohour', selectedCrypto, 24, 1)
    .then(cryptoChartData => {
        const data = cryptoChartData.Data.map(item => ({
            x: item.time,
            y: item.close,
        }));
        this.setState({ cryptoChartData: data });
    });

edited Dec 17, 2021 at 22:43

answered Dec 17, 2021 at 22:32

Narek Ghazaryan

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5 Comments

Frank Boccia Over a year ago

But I am doing this return this.setState({cryptoChartData: data});

Narek Ghazaryan Over a year ago

You don't need that return. You need to use the return inside the mapping.

Frank Boccia Over a year ago

how will it get the cryptoChartData state get updated ? if its not set?

Narek Ghazaryan Over a year ago

I meant only the return. You still need to call the this.setState({cryptoChartData: data});

Frank Boccia Over a year ago

Thank you, it worked perfectly, why was the way I was doing it wrong?

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