updateNumberOnScrollCalculation

const DATA_POINTS_ON_SCREEN = 6;
const WIDTH = Math.round((DATA.length / DATA_POINTS_ON_SCREEN) * Dimensions.get('window').width);

calculateXPosition = (index: number): number => {
    const linearScale = scaleLinear()
        .domain([0, DATA.length])
        .range([0, WIDTH]);

    return linearScale(index);
}

_updateDataPointOnGraph = (event) => {
    const { pinIndex } = this.state;
    const scrollPos = event.nativeEvent.contentOffset.x;
    const index = pinIndex + 1;

    if (scrollPos > this.calculateXPosition(index)) {
        this.setState({ pinIndex: this.state.pinIndex + 1 });
    } if (scrollPos < this.calculateXPosition(index) && scrollPos < this.calculateXPosition(index - 1)) {
        this.setState({ pinIndex: this.state.pinIndex - 1 });
    }
}

const DIMENSION_WIDTH * ((data.length - DATA_POINTS_ON_SCREEN) / (DATA_POINTS_ON_SCREEN - 1) + 1);