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演算子

$trunc (aggregation)

項目一覧

定義

$trunc

$trunc truncates a number to a whole integer or to a specified decimal place.

構文

$trunc演算子の構文は次のとおりです。

{ $trunc : [ <number>, <place> ] }
フィールド
タイプ
説明

<number>

数値

Can be any valid 式 that resolves to a number. Specifically, the expression must resolve to an integer, double, decimal, or long.

$trunc returns an error if the expression resolves to a non-numeric data type.

<place>

integer

任意 Can be any valid 式 that resolves to an integer between -20 and 100, exclusive. For example, -20 < place < 100. Defaults to 0 if unspecified.

  • If <place> resolves to a positive integer, $trunc truncates to <place> decimal places.

    たとえば、 $trunc : [1234.5678, 2] truncates to two decimal places and returns 1234.56.

  • If <place> resolves to a negative integer, $trunc replaces <place> digits left of the decimal with 0.

    たとえば、 $trunc : [1234.5678, -2] replaces to two digits left of the decimal with 0 and returns 1200.

  • If the absolute value of <place> exceeds the number of digits to the left of the decimal, $trunc returns 0.

    たとえば、 $trunc : [ 1234.5678, -5] specifies the fifth digit left of the decimal. This exceeds the number of digits left of the decimal and returns 0.

  • If <place> resolves to 0, $trunc truncates all digits to the right of the decimal and returns the whole integer value.

    たとえば、 $trunc : [1234.5678, 0] returns 1234

<number>式は、数値に変換される限り、どのような有効な式でもかまいません。 式の詳細については、「式演算子 」を参照してください。

動作

$trunc does not round the truncated data. To round input values to a specified place, use the $round expression.

Returned Data Type

The returned data type matches the data type of the input expression or value.

null、NaN、+/- Infinity

  • If the argument resolves to a value of null or refers to a field that is missing, $trunc returns null.

  • If the argument resolves to NaN, $trunc returns NaN.

  • If the argument resolves to negative or positive infinity, $trunc returns negative or positive infinity respectively.

例
結果

{ $trunc: [ NaN, 1] }

NaN

{ $trunc: [ null, 1] }

null

{ $trunc : [ Infinity, 1 ] }

Infinity

{ $trunc : [ -Infinity, 1 ] }

-Infinity

例

次のドキュメントを含むsamplesという名前のコレクションを作成します。

db.samples.insertMany(
   [
      { _id: 1, value: 19.25 },
      { _id: 2, value: 28.73 },
      { _id: 3, value: 34.32 },
      { _id: 4, value: -45.34 }
   ]
)

  • The following aggregation returns value truncated to the first decimal place:

    db.samples.aggregate([
       { $project: { truncatedValue: { $trunc: [ "$value", 1 ] } } }
    ])

    この操作は次の結果を返します。

    { "_id" : 1, "truncatedValue" : 19.2 }
    { "_id" : 2, "truncatedValue" : 28.7 }
    { "_id" : 3, "truncatedValue" : 34.3 }
    { "_id" : 4, "truncatedValue" : -45.3 }

  • The following aggregation returns value truncated to the first place:

    db.samples.aggregate([
       { $project: { truncatedValue: { $trunc: [ "$value", -1 ] } } }
    ])

    この操作は次の結果を返します。

    { "_id" : 1, "truncatedValue" : 10 }
    { "_id" : 2, "truncatedValue" : 20 }
    { "_id" : 3, "truncatedValue" : 30 }
    { "_id" : 4, "truncatedValue" : -40 }

  • The following aggregation returns``value`` truncated to the whole integer:

    db.samples.aggregate([
       { $project: { truncatedValue: { $trunc: [ "$value", 0 ] } } }
    ])

    この操作は次の結果を返します。

    { "_id" : 1, "truncatedValue" : 19 }
    { "_id" : 2, "truncatedValue" : 28 }
    { "_id" : 3, "truncatedValue" : 34 }
    { "_id" : 4, "truncatedValue" : -45 }

戻る

$trim

次へ

$type