Migrating csv data as array into multi-field How do I migrate a sequence of data into a multi-value field?

I am learning D8 migration and working on a large CSV of historic census data from around the world. Example below:

id,Country Name,Country Code,Indicator Name,Indicator Code,1960,1961,1962,1963,1964,1965,1966,1967,1968,1969,1970,1971,1972,1973,1974,1975,1976,1977,1978,1979,1980,1981,1982,1983,1984,1985,1986,1987,1988,1989,1990,1991,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2018
1,Aruba,ABW,"Population, total",SP.POP.TOTL,54211,55438,56225,56695,57032,57360,57715,58055,58386,58726,59063,59440,59840,60243,60528,60657,60586,60366,60103,59980,60096,60567,61345,62201,62836,63026,62644,61833,61079,61032,62149,64622,68235,72504,76700,80324,83200,85451,87277,89005,90853,92898,94992,97017,98737,100031,100834,101222,101358,101455,101669,102046,102560,103159,103774,104341,104872,105366,105845


My migration yml file is as follows:

uuid: 6c54b8f4-96c7-4678-8919-b20c8b318c82
langcode: en
status: true
dependencies: {  }
id: World_Census_Data
class: null
field_plugin_method: null
cck_plugin_method: null
migration_tags:
  - CSV
migration_group: random_migrations
label: 'International census csv data'
source:
  plugin: csv
  path: /var/www/random-migrations/modules/custom/random_migrations/sources/census-58-years.csv
  ids:
    - id
  delimiter: ','
  track_changes: true
process:
  type:
    plugin: default_value
    default_value: census
  title: 'Country Name'
  field_country_code: 'Country Code'
  field_count:
    plugin: array_build
    default_value: 0
    value:
      - 1960
      - 1961
destination:
  plugin: 'entity:node'
migration_dependencies: {}


Instead of manually creating an individual field for each year, I created the field_count field which is an Interger field set to allow unlimited entries. My idea is to import all the population numbers from 1960 to 2018 as new entries of field_count for each country.

My problem is the population data is not being imported. Can anyone advice if my proposed solution possible and if it is, what I need to change/fix in my yml to get my migration working?

Help, please.
I figured it out.
The issue was the plugin. Rather than * array_build*, I should have been using the get plugin, as follows:

process:
  type:
    plugin: default_value
    default_value: census
  title: 'Country Name'
  field_country_code: 'Country Code'
  field_count:
    plugin: get
    default_value: 0
    source:
      - 1960
      - 1961
      - 1962
     .
     .
     .


That migrates the value of the array indexed by those years into the field_count field. And because the field has multiple cardinality, each row is written in as a new value.