How To Scan On Past Dates

[VR555]

I'm struggling to figure how to use this scan
https://usethinkscript.com/threads/useful-indicators-for-swing-trading-with-thinkorswim.15068/
on past dates. Is there a way to 'look back'?

 

[antwerks]

I'm struggling to figure how to use this scan on past dates. Is there a way to 'look back'?

WOW great question and I see where you are going with that - I do not know if TOS has that capability. A good question for one of the TOS experts.... @merryDay

 

[VR555]

@antwerks - Here’s what I got from a Google search, and since I don’t have good coding skills, I’m hoping that you can take this example and apply it to your scan that will allow me to look at past dates:

Select thinkScript Editor instead of the wizard

Use array indexing to tell the scanner how many bars in the past to look at. For example, close[20]represents the closing price exactly 20 days ago. [, 2]

Example Script (Scanning for a 52-week high 20 days ago):

thinkscript
plot Scan = high[20] == Highest(high[20], 252);

 

[antwerks]

@antwerks - Here’s what I got from a Google search, and since I don’t have good coding skills, I’m hoping that you can take this example and apply it to your scan that will allow me to look at past dates:

Select thinkScript Editor instead of the wizard

Use array indexing to tell the scanner how many bars in the past to look at. For example, close[20]represents the closing price exactly 20 days ago. [, 2]

Example Script (Scanning for a 52-week high 20 days ago):

thinkscript
plot Scan = high[20] == Highest(high[20], 252);

let me play with that- thanks

 

[halcyonguy]

scans work on data on the last bar.
so... you could make a study that , reads old data, and if the data is what you want, set a plot variable to true, on the last bar.
then add that study to the scan rules.

 

[VR555]

scans work on data on the last bar.
so... you could make a study that , reads old data, and if the data is what you want, set a plot variable to true, on the last bar.
then add that study to the scan rules.

Id do that if I had the background and skills necessary - thanks for the info.

 

[antwerks]

Id do that if I had the background and skills necessary - thanks for the info.

Three useful historical-scan patterns
1. Condition happened within the last X bars
This is the simplest and usually best:

input lookbackBars = 10;

def condition =
    close crosses above ExpAverage(close, 21);

plot scan =
    Highest(
        if condition then 1 else 0,
        lookbackBars
    ) > 0;

This returns symbols where the condition occurred at least once during the last 10 bars.
The equivalent scanner concept is “condition was true within X bars,” which ThinkOrSwim also supports through its condition tools.

2. Condition happened previously and remains valid now

This is probably more useful for your swing scanner.
Example:

• EMA reclaim occurred during the last 10 bars.
• Price is still above the EMA now.
• Trend has not failed.

input emaLength = 21;
input lookbackBars = 10;

def ema21 = ExpAverage(close, emaLength);

def freshReclaim =
    close > ema21 and
    close[1] <= ema21[1];

def reclaimOccurred =
    Highest(
        if freshReclaim then 1 else 0,
        lookbackBars
    ) > 0;

def stillValid =
    close > ema21 and
    ema21 > ema21[1];

plot scan =
    reclaimOccurred and
    stillValid;

This does not merely find an old signal. It checks that the historical setup is still tradable today.

3). Record a historical event and carry its state forward
Use a recursive variable when the signal should remain active until invalidated:

input emaLength = 21;

def ema21 = ExpAverage(close, emaLength);

def trigger =
    close crosses above ema21;

def invalidate =
    close crosses below ema21;

rec setupActive =
    if BarNumber() == 1 then 0
    else if trigger then 1
    else if invalidate then 0
    else setupActive[1];

plot scan = setupActive;

This creates memory:

• Trigger occurs.
• setupActive remains true.
• It stays true until the invalidation occurs.

That is especially useful for forex trading tool because it can remember that a tradable condition began several bars ago without requiring the trigger to happen on the current bar. It works for all tradable tickers.

For all of these you will have to input your criteria you are looking for in the script.

 

[Joshua]

@VR555 A dynamic number of days ago, or a specific date?

 

[antwerks]

@VR555 A dynamic number of days ago, or a specific date?

Dynamic in the sense you can set it

 

[VR555]

Dynamic in the sense you can set it

That’s just what I was looking for. As always, you are the GREAT one!

 

[VR555]

Three useful historical-scan patterns
1. Condition happened within the last X bars
This is the simplest and usually best:

input lookbackBars = 10;

def condition =
    close crosses above ExpAverage(close, 21);

plot scan =
    Highest(
        if condition then 1 else 0,
        lookbackBars
    ) > 0;

This returns symbols where the condition occurred at least once during the last 10 bars.
The equivalent scanner concept is “condition was true within X bars,” which ThinkOrSwim also supports through its condition tools.

2. Condition happened previously and remains valid now

This is probably more useful for your swing scanner.
Example:

• EMA reclaim occurred during the last 10 bars.
• Price is still above the EMA now.
• Trend has not failed.

input emaLength = 21;
input lookbackBars = 10;

def ema21 = ExpAverage(close, emaLength);

def freshReclaim =
    close > ema21 and
    close[1] <= ema21[1];

def reclaimOccurred =
    Highest(
        if freshReclaim then 1 else 0,
        lookbackBars
    ) > 0;

def stillValid =
    close > ema21 and
    ema21 > ema21[1];

plot scan =
    reclaimOccurred and
    stillValid;

This does not merely find an old signal. It checks that the historical setup is still tradable today.

3). Record a historical event and carry its state forward
Use a recursive variable when the signal should remain active until invalidated:

input emaLength = 21;

def ema21 = ExpAverage(close, emaLength);

def trigger =
    close crosses above ema21;

def invalidate =
    close crosses below ema21;

rec setupActive =
    if BarNumber() == 1 then 0
    else if trigger then 1
    else if invalidate then 0
    else setupActive[1];

plot scan = setupActive;

This creates memory:

• Trigger occurs.
• setupActive remains true.
• It stays true until the invalidation occurs.

That is especially useful for forex trading tool because it can remember that a tradable condition began several bars ago without requiring the trigger to happen on the current bar. It works for all tradable tickers.

For all of these you will have to input your criteria you are looking for in the script.

A couple of questions:
1 - do I add one of these at the bottom of an existing scan’s script?
2 - how can I verify it was on the date intended to look back at?

 

[antwerks]

A couple of questions:
1 - do I add one of these at the bottom of an existing scan’s script?
2 - how can I verify it was on the date intended to look back at?

No they run on their own and unless it is encompassed withing the lookback period - we could scan date specific - let me think about the