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Clear[P1, P2, B1, B2, P3, B3] Clear[P1comb, P2comb, B1comb, B2comb, P3comb, B3comb] a = {P1, P2, B1, B2, P3, B3}; b = {P1comb, P2comb, B1comb, B2comb, P3comb, B3comb}; 

Using lower-case count initially, to be replaced with Count

Array[With[{c = b[[#]]}, c = f[a[[#]]] - count[Take[a, # - 1], a[[#]]]] &, Length[a]] 

Examples

P1comb 

-count[{}, P1] + f[P1] 

B3comb 

-count[{P1, P2, B1, B2, P3}, B3] + f[B3] 

Assigning values after symbolic construction.

With[{d = a}, d = {1, 2, 3, 4, 3, 2}]; B2 

4 

B3comb /. count -> Count 

-1 + f[2] 

Clear[P1, P2, B1, B2, P3, B3] Clear[P1comb, P2comb, B1comb, B2comb, P3comb, B3comb] a = {P1, P2, B1, B2, P3, B3}; b = {P1comb, P2comb, B1comb, B2comb, P3comb, B3comb}; 

Using lower-case count initially, to be replaced with Count

Array[With[{c = b[[#]]}, c = f[a[[#]]] - count[Take[a, # - 1], a[[#]]]] &, Length[a]] 

Examples

P1comb 

-count[{}, P1] + f[P1] 

B3comb 

-count[{P1, P2, B1, B2, P3}, B3] + f[B3] 

Assigning values after symbolic construction.

With[{d = a}, d = {1, 2, 3, 4, 3, 2}]; B2 

4 

b /. count -> Count 

{f[1], f[2], f[3], f[4], -1 + f[3], -1 + f[2]} 

Clear[P1comb, P2comb, B1comb, B2comb, P3comb, B3comb] a = {P1, P2, B1, B2, P3, B3}; b = {P1comb, P2comb, B1comb, B2comb, P3comb, B3comb}; 

Using lower-case count to illustrate the output. (Replace with Count.)

Array[With[{c = b[[#]]}, c = f[a[[#]]] - count[Take[a, # - 1], a[[#]]]] &, Length[a]] 

Example output

P1comb 

-count[{}, P1] + f[P1] 

B3comb 

-count[{P1, P2, B1, B2, P3}, B3] + f[B3] 

Clear[P1, P2, B1, B2, P3, B3] Clear[P1comb, P2comb, B1comb, B2comb, P3comb, B3comb] a = {P1, P2, B1, B2, P3, B3}; b = {P1comb, P2comb, B1comb, B2comb, P3comb, B3comb}; 

Using lower-case count initially, to be replaced with Count

Array[With[{c = b[[#]]}, c = f[a[[#]]] - count[Take[a, # - 1], a[[#]]]] &, Length[a]] 

Examples

P1comb 

-count[{}, P1] + f[P1] 

B3comb 

-count[{P1, P2, B1, B2, P3}, B3] + f[B3] 

Assigning values after symbolic construction.

With[{d = a}, d = {1, 2, 3, 4, 3, 2}]; B2 

4 

B3comb /. count -> Count 

-1 + f[2] 

Clear[P1comb, P2comb, B1comb, B2comb, P3comb, B3comb] a = {P1, P2, B1, B2, P3, B3}; b = {P1comb, P2comb, B1comb, B2comb, P3comb, B3comb}; 

Using lower-case count to illustrate the output. (Replace with Count.)

Array[With[{c = b[[#]]}, c = f[a[[#]]] - count[Take[a, # - 1], a[[#]]]] &, Length[a]] 

E.g.

B3comb

-count[{P1, P2, B1, B2, P3}, B3] + f[B3] 

Clear[P1comb, P2comb, B1comb, B2comb, P3comb, B3comb] a = {P1, P2, B1, B2, P3, B3}; b = {P1comb, P2comb, B1comb, B2comb, P3comb, B3comb}; 

Using lower-case count to illustrate the output. (Replace with Count.)

Array[With[{c = b[[#]]}, c = f[a[[#]]] - count[Take[a, # - 1], a[[#]]]] &, Length[a]] 

Example output

P1comb 

-count[{}, P1] + f[P1] 

B3comb 

-count[{P1, P2, B1, B2, P3}, B3] + f[B3]