# SubIndex

(Redirected from Subindex)

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SubIndex is used to find a value in an array.

## SubIndex(a, u, i, first)

Assuming array «a» has index «i», it returns the value of «i» for which «a» [«i»] = «u». If there is no match for «u» in «a», it returns Null. If there are multiple matches, it returns the last value of «i». If «a» has index(es) in addition to «i», or if «u» is an array with other indexes, those indexes also appear in the result.

(New to Analytica 5.2) When «u» occurs more than once in «a», it finds the last occurrence unless the optional «first» parameter is true.

Subindex is similar to Vlookup and Hlookup in Excel.

SubIndex is the inverse of SubScript: Where SubScript maps from the index value to the array value, SubIndex maps from the array value to the index value. SubIndex is not as efficient as SubScript -- SubScript uses a hash-table for constant-time associative lookup, but SubIndex must search the array for the indicated value, which takes time linear in the size of the array.

## Example

Variable A :=
I ▶
'a' 'b' 'c' 'd' 'e' 'f'
4 3 2 5 3 1
SubIndex(A, 2, I) → 'c'
SubIndex(A, 3, I) → 'e'
SubIndex(A, 6, I) → «null»
SubIndex(A, 1..5, I) → ['f', 'c', 'e', 'a', 'd']

## Details & More Examples

### Array abstraction

When «a» has more than one dimension, or «u» is an array, SubIndex array abstracts according to the standard rules of array abstraction. For example, when «a» contains an index other than «i», SubIndex is applied to each slice of that index, returning the position of «u» in the corresponding slice. When «u» contains an array of values, the position of each of those values in «a» is returned.

### Example 1

Define variable A as above and let:

Variable B :=
I ▶
J ▼ 'a' 'b' 'c' 'd' 'e' 'f'
1 3 5 2 4 5 3
2 2 1 5 2 3 4
Variable C :=
K ▶
1 2 3 4 5
4 2 5 1 3

Then:

SubIndex(B, 2, I) →
J ▶
1 2
'c' 'd'
SubIndex(A, C, I) →
K ▶
1 2 3 4 5
'a' 'c' 'd' 'f' 'e'

If «u» is an array of values, in this case the variable C, an array is returned:

SubIndex(B, C, I) →
K ▶
J ▼ 1 2 3 4 5
1 'd' 'c' 'e' «null» 'f'
2 'f' 'd' 'c' 'd' 'e'

### Example 2

The following example can be found in the User Guide Examples.

Let:

Variable Car_prices :=
Years ▶
Car_type ▼ 2005 2006 2007 2008 2009
VW $16,000$17,000 $18,000$19,000 $20,000 Honda$18,000 $19,000$20,000 $22,000$24,000
BMW $25,000$26,000 $28,000$30,000 \$32,000
Index Car_type := ['VW', 'Honda', 'BMW']

Then:

SubIndex(Car_prices, 18K, Car_type) →
Years ▶
2005 2006 2007 2008 2009
Honda «null» VW «null» «null»
SubIndex(Car_prices, 18K, Years) →
Car_type ▶
VW Honda BMW
2007 2005 «null»
SubIndex(Car_prices, [18K, 19K] Car_type) →
Years ▶
2005 2006 2007 2008 2009
Honda «null» VW «null» «null»
«null» Honda «null» VW «null»