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MovingMap (new in version 10) applies a function to discrete data over a moving window. This is very convenient for calculating the percentage change of a series.

But the error returned by the following code bothers me:

series = Range[5];
MovingMap[#[[2]]/#[[1]] - 1 &, series, {2}]

(* Power::infy: Infinite expression 1/0. encountered. >>\*)
(* {1, 1/2, 1/3, 1/4} *)

However, this code returns the result with no error:

MovingMap[f, series, {2}] /. f -> Function[#[[2]]/#[[1]] - 1]

(* {1, 1/2, 1/3, 1/4} *)

What causes this problem?

Bug introduced in 10.0 and fixed in 10.1

MovingMap (new in version 10) applies a function to discrete data over a moving window. This is very convenient for calculating the percentage change of a series.

But the error returned by the following code bothers me:

series = Range[5];
MovingMap[#[[2]]/#[[1]] - 1 &, series, {2}]

(* Power::infy: Infinite expression 1/0. encountered. >>\*)
(* {1, 1/2, 1/3, 1/4} *)

However, this code returns the result with no error:

MovingMap[f, series, {2}] /. f -> Function[#[[2]]/#[[1]] - 1]

(* {1, 1/2, 1/3, 1/4} *)

What causes this problem?

MovingMap is a very convenient tool to calculate the percentage changes of a series.

But one thing bothers me is this error.

series = Range[5];
MovingMap[#[[2]]/#[[1]] - 1 &, series, {2}]

The output is

Power::infy: Infinite expression 1/0. encountered. >>
{1, 1/2, 1/3, 1/4}

However,

MovingMap[f, series, {2}] /. f -> Function[#[[2]]/#[[1]] - 1]

gives

{1, 1/2, 1/3, 1/4}

without an error.

I don't understand what causes that problem.

MovingMap (new in version 10) applies a function to discrete data over a moving window. This is very convenient for calculating the percentage change of a series.

But the error returned by the following code bothers me:

series = Range[5];
MovingMap[#[[2]]/#[[1]] - 1 &, series, {2}]

(* Power::infy: Infinite expression 1/0. encountered. >>\*)
(* {1, 1/2, 1/3, 1/4} *)

However, this code returns the result with no error:

MovingMap[f, series, {2}] /. f -> Function[#[[2]]/#[[1]] - 1]

(* {1, 1/2, 1/3, 1/4} *)

What causes this problem?