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BlockRandom[expr]

evaluates expr with all pseudorandom generators localized, so that uses of SeedRandom, RandomInteger, and related functions within the evaluation of expr do not affect subsequent pseudorandom sequences.

Details and Options
Details and Options Details and Options
Examples  
Basic Examples  
Scope  
Options  
RandomSeeding  
Applications  
Properties & Relations  
See Also
Tech Notes
Related Guides
History
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BlockRandom

BlockRandom[expr]

evaluates expr with all pseudorandom generators localized, so that uses of SeedRandom, RandomInteger, and related functions within the evaluation of expr do not affect subsequent pseudorandom sequences.

Details and Options

  • BlockRandom[expr] in effect saves the states of all pseudorandom generators before evaluating expr, then restores them afterwards.
  • BlockRandom[expr] always gives the same result as just evaluating expr, though it can affect values obtained for subsequent expressions.
  • BlockRandom[expr,RandomSeeding->seeding] specifies that the random generators should be seeded with the specified seeding before evaluating expr.
  • BlockRandom has attribute HoldFirst.
  • Many built-in functions in the Wolfram Language effectively use BlockRandom.

Examples

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Basic Examples  (2)

Use BlockRandom to localize the use of a pseudorandom generator:

Wolfram Language code: {RandomReal[], BlockRandom[RandomReal[]], RandomReal[], RandomReal[]}

Use BlockRandom to prevent one use of a randomized algorithm from affecting others:

Wolfram Language code: Table[Total[RandomInteger[1, 100]], {20}]
Wolfram Language code: Table[BlockRandom[Total[RandomInteger[1, 100]]], {20}]

Scope  (1)

BlockRandom works with all pseudorandom generators in the Wolfram Language:

Wolfram Language code: Table[BlockRandom[RandomReal[1, 2]], {3}]
Wolfram Language code: Table[BlockRandom[RandomChoice[{a, b, c}, 5]], {3}]

Options  (3)

RandomSeeding  (3)

Use a particular random seed to ensure predictable results:

Wolfram Language code: Table[BlockRandom[RandomInteger[9, 10]], {2}]
Wolfram Language code: Table[BlockRandom[RandomInteger[9, 10], RandomSeeding -> 1234], {2}]

When a generator is used outside BlockRandom, the results without seeding are changed:

Wolfram Language code: RandomInteger[9, 10]
Wolfram Language code: Table[BlockRandom[RandomInteger[9, 10]], {2}]
Wolfram Language code: Table[BlockRandom[RandomInteger[9, 10], RandomSeeding -> 1234], {2}]

Use a RandomGeneratorState object to simultaneously specify the seed and method:

Wolfram Language code: BlockRandom[RandomReal[1, 5], RandomSeeding -> RandomGeneratorState[{"ExtendedCA", {80, 4, 0}}, {{NumericArray[{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, "UnsignedInteger64"], 0, 20, 20}, {RawArray["UnsignedInteger64", {8402553920425805686, 9934563772124633544, 13 ... 91188148046, 1589259630949761215, 10047890358231901395, 5864488619226313396, 17324547311914965925, 9027643525916071240, 2022314520320920354, 9575528438213517111}], 4, 0}}, NumericArray[{6155169294560358013, 0}, "UnsignedInteger64"]]]

Use Automatic seeding to get different results every time:

Wolfram Language code: Table[BlockRandom[RandomInteger[9, 10]], {4}]
Wolfram Language code: Table[BlockRandom[RandomInteger[9, 10], RandomSeeding -> Automatic], {4}]

Applications  (2)

Run a randomized algorithm without affecting other random sequences:

Wolfram Language code: SeedRandom[1234];RandomReal[1, 5]
Wolfram Language code: SeedRandom[1234];

Compute a Monte Carlo approximation to :

Wolfram Language code: BlockRandom[4.0 Mean[Table[Boole[Norm[RandomReal[1, 2]] < 1], {10 ^ 4}]]]

BlockRandom prevents other random sequences from being affected:

Wolfram Language code: RandomReal[1, 5]

Get the "same" random number at different precisions:

Wolfram Language code: Table[BlockRandom[RandomReal[WorkingPrecision -> p]], {p, 10}]

Properties & Relations  (1)

BlockRandom effectively does the same as resetting the random seed to its previous value:

Wolfram Language code: {SeedRandom[123];RandomReal[], SeedRandom[123];RandomReal[]}
Wolfram Language code: {SeedRandom[123];BlockRandom[RandomReal[]], RandomReal[]}
Wolfram Research (2007), BlockRandom, Wolfram Language function, https://reference.wolfram.com/language/ref/BlockRandom.html (updated 2017).

Text

Wolfram Research (2007), BlockRandom, Wolfram Language function, https://reference.wolfram.com/language/ref/BlockRandom.html (updated 2017).

CMS

Wolfram Language. 2007. "BlockRandom." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2017. https://reference.wolfram.com/language/ref/BlockRandom.html.

APA

Wolfram Language. (2007). BlockRandom. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/BlockRandom.html

BibTeX

@misc{reference.wolfram_2026_blockrandom, author="Wolfram Research", title="{BlockRandom}", year="2017", howpublished="\url{https://reference.wolfram.com/language/ref/BlockRandom.html}", note=[Accessed: 12-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_blockrandom, organization={Wolfram Research}, title={BlockRandom}, year={2017}, url={https://reference.wolfram.com/language/ref/BlockRandom.html}, note=[Accessed: 12-June-2026]}